Long QT Syndrome: Symptoms, Causes & Treatment Guide
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
Long QT syndrome (LQTS) is a heart rhythm disorder in which the heart's electrical system takes longer than usual to recharge between beats. This delay can trigger fast, chaotic heartbeats that are life-threatening, with sudden fainting as the most common warning sign. It can be inherited from birth or develop later from certain medicines or mineral imbalances — and in the acquired form, it is often reversible. Diagnosis is made with an electrocardiogram (ECG), sometimes with heart monitors or genetic testing. Treatment ranges from lifestyle changes and beta blocker medicines to devices and surgery for higher-risk cases.
Quick Answer
What is long QT syndrome? A heart rhythm disorder where the heart takes longer than usual to recover between beats, causing fast, chaotic, potentially life-threatening heartbeats.
Most common symptom: Sudden fainting (syncope), often with little to no warning.
Two types: Congenital (inherited through DNA) and acquired (caused by medicines or health conditions).
Who is at risk: People with a family history of LQTS, those taking QT-prolonging medicines, and anyone with low potassium, calcium, or magnesium.
How it's diagnosed: Primarily with an ECG (electrocardiogram); heart monitors, exercise stress tests, and genetic testing may follow.
How it's treated: Lifestyle changes, beta blockers (such as nadolol or propranolol), stopping triggering medicines, and in some cases an implantable defibrillator or nerve surgery.
Can you live an active life? Many people stay fully active — including competitive sports — after discussing safe activities with their healthcare team.
What Is Long QT Syndrome?
Long QT syndrome (LQTS) is a heart rhythm disorder that causes fast, chaotic heartbeats. These irregular heartbeats can be life-threatening.
LQTS affects the electrical signals that travel through the heart and cause it to beat — not the shape or form of the heart itself.
Some people are born with DNA changes that cause long QT syndrome. This is known as congenital long QT syndrome. LQTS can also develop later in life because of certain health conditions, medicines, or changes in the body's mineral levels. That form is called acquired long QT syndrome.
LQTS can cause sudden fainting and seizures. Young people with the condition carry a higher risk of sudden cardiac death.
The good news: treatment — including lifestyle changes and medicines — can prevent the dangerous heartbeats. Sometimes a medical device or surgery is needed.
What Are the Symptoms of Long QT Syndrome?
The most common symptom of long QT syndrome is fainting, also called syncope (a temporary loss of consciousness). An LQTS fainting spell can strike with little to no warning.
Fainting happens when the heart beats irregularly for a short time. You might faint when you are excited, angry, or scared — or during exercise. If you have LQTS, things that startle you can make you pass out, such as a loud ringtone or an alarm clock.
Before fainting, some people notice warning signs, and long QT syndrome can also cause seizures in some people. The main symptoms include:
Fainting (syncope): a sudden loss of consciousness with little to no warning — the most common LQTS symptom.
Palpitations: a pounding or racing heartbeat, often a warning sign before fainting.
Lightheadedness: feeling dizzy or unsteady, often before a fainting spell.
Blurred vision: vision dims or goes hazy, often before a fainting spell.
Weakness: unusual tiredness or loss of strength.
Seizures: full-body convulsions, caused by the brain temporarily lacking blood.
When do symptoms appear?
Babies born with LQTS may show symptoms during their first weeks or months of life. Sometimes symptoms begin later in childhood. Most people born with LQTS have symptoms by age 40. Symptoms can even happen during sleep.
Importantly, some people have no symptoms at all. The disorder may be found during a heart test called an electrocardiogram (ECG), or discovered through genetic testing done for other reasons.
When to see a doctor
Make an appointment for a health checkup if you faint or if you feel a pounding or fast heartbeat.
Family history matters. Tell your healthcare team if a parent, brother, sister, or child has long QT syndrome. LQTS can run in families, which means it can be inherited.
What Causes Long QT Syndrome?
LQTS is caused by changes in the heart's electrical signaling system. It does not affect the shape or form of the heart.
Here is how a healthy heart works. The heart sends blood to the body with each heartbeat. The chambers squeeze and relax to pump the blood, and the heart's electrical system controls this coordinated action. Electrical signals called impulses move from the top to the bottom of the heart, telling it when to squeeze and beat. After each heartbeat, the system recharges to prepare for the next one.
In long QT syndrome, the heart's electrical system takes longer than usual to recover between beats. This delay is called a prolonged QT interval.
Long QT syndrome usually falls into two groups:
Congenital long QT syndrome: you are born with it. It is caused by DNA changes passed down through families (inherited).
Acquired long QT syndrome: it develops later, caused by another health condition or a medicine. It usually can be reversed when the specific cause is found and treated.
Causes of congenital long QT syndrome
Many genes and gene changes have been linked to LQTS. There are two inherited types:
Romano-Ward syndrome: passed on by one changed gene from one parent (autosomal dominant); the more common type.
Jervell and Lange-Nielsen syndrome: passed on by changed genes from both parents (autosomal recessive); rare, very early onset, severe — children also are deaf.
Causes of acquired long QT syndrome
A medicine or another health condition can cause acquired LQTS. When a medicine is the cause, it is sometimes called drug-induced long QT syndrome. More than 100 medicines can cause prolonged QT intervals in otherwise healthy people, including:
Some antibiotics, such as erythromycin and azithromycin.
Some antifungal medicines used for yeast infections.
Water pills (diuretics) that cause the body to lose too much potassium or other minerals.
Anti-arrhythmics — heart rhythm medicines that can lengthen the QT interval.
Some medicines for anxiety and depression.
Some medicines for an upset stomach.
Always tell your healthcare professional about every medicine you take — including those bought without a prescription. Health conditions that can cause acquired LQTS include:
Hypothermia: body temperature below 95°F (35°C).
Hypocalcemia, hypomagnesemia, hypokalemia: low calcium, magnesium, or potassium.
Pheochromocytoma: an adrenal gland tumor that usually is not cancer.
Stroke or brain bleed.
Hypothyroidism: underactive thyroid.
What Increases Your Risk of Long QT Syndrome?
Several factors raise the chance of long QT syndrome:
A history of cardiac arrest.
Having a parent, brother, sister, or child with long QT syndrome.
Using medicines known to prolong the QT interval.
Being assigned female at birth and taking certain heart medicines.
Frequent vomiting or diarrhea, which can change body minerals such as potassium.
Eating disorders such as anorexia nervosa, which also alter mineral levels.
If you have long QT syndrome and want to become pregnant, tell your healthcare professional. Your care team will check you carefully during pregnancy to help prevent triggers of LQTS symptoms.
What Are the Complications of Long QT Syndrome?
Usually, after an LQTS episode, the heart returns to a regular rhythm on its own. But sudden cardiac death can happen if the heart rhythm is not quickly corrected. Sometimes treatment is needed to reset the rhythm. The main complications are:
Torsades de pointes ("twisting of the points"): a life-threatening fast heartbeat in which the heart's two lower chambers beat fast and out of rhythm. The heart pumps out less blood, and the lack of blood to the brain causes sudden fainting, often without warning. If it lasts a long time, fainting can be followed by a full-body seizure, and it can progress to ventricular fibrillation if it does not correct itself.
Ventricular fibrillation: an irregular heartbeat in which the lower chambers beat so fast that the heart trembles and stops pumping blood. Unless a defibrillator quickly resets the rhythm, brain damage and death can follow.
Sudden cardiac death: the swift, unexpected end of all heart activity. LQTS has been linked to sudden cardiac death in young people who otherwise appear healthy, and it may explain some unexplained fainting, drownings, or seizures in children and young adults.
Proper medical treatment and lifestyle changes can help prevent these complications.
How Is Long QT Syndrome Diagnosed?
A healthcare professional starts with a physical exam — asking about your symptoms, medical history, and family history, and listening to your heart with a stethoscope. If an irregular heartbeat is suspected, tests confirm the diagnosis.
The main test: the electrocardiogram (ECG or EKG)
An ECG is the most common test used to diagnose LQTS. It records the heart's electrical signals and shows how fast or slow the heart is beating. Sticky patches called electrodes attach to the chest — and sometimes the arms and legs — and connect to a computer that displays the results as waves.
An ECG shows five waves: P, Q, R, S, and T. The waves Q through T show the heart signaling in its lower chambers. The time between the start of the Q wave and the end of the T wave is the QT interval — how long it takes the heart to squeeze and refill with blood before beating again. If this takes longer than usual, it is a prolonged QT interval.
An ideal QT interval depends on your age, your sex, and your heart rate. In people who have had torsades de pointes, the waves on the ECG look twisted.
When a regular ECG is not enough
If LQTS symptoms do not happen often, they may not appear on a routine ECG. In that case, your healthcare professional may have you wear a heart monitor at home:
Holter monitor: a small, portable ECG worn for a day or two while you do regular activities.
Event recorder: like a Holter monitor, but it records only for a few minutes at a time. It is typically worn for about 30 days; you push a button when you feel symptoms, and some devices record automatically when an irregular rhythm is detected.
Some personal devices, such as smartwatches, have ECG sensors. Ask your healthcare professional whether this is an option for you.
Additional tests
Exercise stress tests: walking on a treadmill or pedaling a stationary bike while your heart activity is monitored, to see how the heart reacts to physical activity. If you cannot exercise, a medicine that increases the heart rate may be used instead, sometimes alongside an echocardiogram.
Genetic testing: checks for the gene changes that can cause LQTS. If you have LQTS, family members may be advised to get tested too. Genetic testing cannot find every inherited case, so families are encouraged to speak with a genetic counselor before and after testing.
How Is Long QT Syndrome Treated?
Treatment for long QT syndrome may include lifestyle changes, medicines, a medical device, or surgery — depending on your symptoms and your type of LQTS. You may need treatment even if you rarely have symptoms.
The goals of treatment are to prevent irregular heartbeats and to prevent sudden cardiac death.
Therapies
Some people with acquired LQTS receive fluids or minerals — such as magnesium — through a needle in a vein (IV).
Medications
If a medicine is causing LQTS, stopping that medicine may be all the treatment needed. Your healthcare professional can explain how to stop safely. Do not change or stop any medicines without talking to your healthcare team. Medicines used to treat long QT syndrome include:
Beta blockers (nadolol, propranolol): slow the heart rate and reduce the chances of a long QT episode.
Mexiletine: taken with a beta blocker, it may shorten the QT interval and lower the risk of fainting, seizure, or sudden cardiac death.
Surgery or procedures
Some people need surgery or a device to control the heartbeat:
Left cardiac sympathetic denervation (LCSD) surgery: used when LQTS causes continuing rhythm changes and beta blockers do not work. It does not cure LQTS — it lowers the risk of sudden cardiac death. Surgeons remove specific nerves along the left side of the spine that help control the heart rhythm.
Implantable cardioverter-defibrillator (ICD): a device placed under the skin near the collarbone that continuously checks the heart rhythm and sends low- or high-energy shocks to reset it if needed. Most people with LQTS do not need an ICD; it may be suggested for some athletes returning to competitive sports. Discuss the benefits and risks with your healthcare team.
Lifestyle and Home Habits: Living Safely with Long QT Syndrome
Your healthcare professional may suggest lifestyle changes that lower the risk of a fainting spell or sudden cardiac death:
Know which sports are safe: you may be able to stay fully active — even in competitive sports — but talk to your healthcare team first. Never swim alone, and take someone who can help if you faint.
Check for startling sounds: turn down the volume on doorbells and devices such as phones that may startle you, especially during sleep.
Control emotions: strong excitement, anger, or surprise can trigger heartbeat changes. Exercise, mindfulness, and support groups can reduce stress.
Check your medicines: avoid medicines that prolong the QT interval, and tell your healthcare team about every medicine and supplement you take — even over-the-counter ones.
Get regular health checkups: your care team may update your treatment plan if your symptoms or health change.
Coping and support
Living with a dangerous heart rhythm can cause stress for you and your loved ones. Three practical steps can help:
Tell other people you have LQTS: family, friends, teachers, and neighbors. Wear a medical alert identification so others know.
Have an emergency plan: family members may want to learn CPR, and it may be appropriate to have an AED (automated external defibrillator) available or reachable quickly.
Seek support: support groups let you share experiences with others familiar with LQTS. Families with inherited LQTS may also benefit from a genetic counselor.
Preparing for your appointment
If you have pounding, fast, or irregular heartbeats, make an appointment for a health checkup. You may be referred to a cardiologist (a doctor trained in heart conditions) or an electrophysiologist (a specialist in heart rhythm disorders).
Before the visit, write down your symptoms and how long they have lasted, your other health conditions, the names and doses of your medicines, and any family history of irregular heartbeats or sudden death. While you wait for the appointment, ask family members whether anyone related to you has a history of LQTS or unexplained death.
Can Long QT Syndrome Be Prevented?
There is no known way to prevent congenital LQTS. If someone in your family has it, ask a health professional whether genetic screening is right for you. With proper treatment, you can manage and prevent the dangerous heartbeats that lead to LQTS complications.
Regular health checkups and good communication with your healthcare professional may help prevent the causes of some types of acquired LQTS. It is especially important not to take medicines that can affect the heart rhythm and prolong the QT interval.
Conclusion
Long QT syndrome is a heart rhythm disorder with real dangers — but also a clear path to safety. Its electrical system takes longer than normal to recharge between beats, producing fast, chaotic heartbeats that can cause sudden fainting, seizures, or, without quick correction, sudden cardiac death. It can be inherited from birth or develop later from certain medicines or low mineral levels, and the acquired form is often reversible once the cause is addressed.
The diagnosis rests on a simple heart test — the ECG — and treatment spans lifestyle changes, beta blockers, and, when needed, devices or surgery. Proper medical treatment and daily habits like never swimming alone, managing startling sounds, and checking every medicine with your doctor can dramatically lower the risk of complications.
Have you fainted without warning or felt sudden pounding heartbeats? Talk to a doctor about an ECG — a few minutes of testing can uncover a manageable condition and protect your heart for years to come.
Frequently Asked Questions
Is long QT syndrome dangerous?
Long QT syndrome can cause fast, chaotic heartbeats that are life-threatening, and young people with LQTS have a higher risk of sudden cardiac death. However, proper treatment and lifestyle changes can help prevent dangerous episodes.
What are the warning signs of long QT syndrome?
The most common sign is sudden fainting with little to no warning. Before fainting, some people notice blurred vision, lightheadedness, a pounding heartbeat (palpitations), or weakness. LQTS can also cause seizures, and symptoms can happen during exercise, strong emotions, or sleep.
Can long QT syndrome go away?
The acquired form usually can be reversed once the specific cause — such as a triggering medicine or a mineral imbalance — is found and treated. Congenital LQTS cannot be cured, but treatment can manage and prevent the dangerous heartbeats.
Is long QT syndrome inherited?
Yes, in its congenital form. It is caused by DNA changes passed down through families. If a parent, sibling, or child has LQTS, tell your healthcare team, and ask whether genetic screening is right for you.
How is long QT syndrome diagnosed?
Most often with an ECG (electrocardiogram), which records the heart's electrical waves and measures the QT interval. If symptoms are infrequent, a Holter monitor, event recorder, or exercise stress test may be used, and genetic testing can confirm the diagnosis.
What medicines cause long QT syndrome?
More than 100 medicines can prolong the QT interval in otherwise healthy people, including some antibiotics (such as azithromycin), antifungals, diuretics (water pills), anti-arrhythmic heart medicines, some anxiety and depression drugs, and some stomach medicines. Always tell your healthcare professional about all medicines you take.
Can I play sports with long QT syndrome?
Many people with LQTS can stay fully active, including in competitive sports, after discussing it with their healthcare team. The key safety rule is to never swim alone, and to take someone along for other activities who can help if you faint.
Do I need a defibrillator if I have long QT syndrome?
Most people with LQTS do not need an implantable cardioverter-defibrillator (ICD). It may be suggested when beta blockers do not control continuing rhythm changes, or for some athletes returning to competitive sports. Discuss the benefits and risks with your healthcare team.
References
Symptoms & causes of long QT syndrome (updated July 19, 2024)
Diagnosis & treatment of long QT syndrome (updated July 19, 2024)
Rinnit.com provides general health information for educational purposes. This content does not replace professional medical advice — always consult a qualified healthcare provider for diagnosis and treatment.
Health information, not medical advice. This article is for general education and is not a substitute for professional diagnosis or treatment. Always consult a qualified healthcare provider about your own health, and seek emergency care for urgent symptoms.
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