Cardiac Glycosides: How They Work, What They Treat, and How to Take Them Safely
Updated: 6 days ago
Written and medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 31, 2026 · How we review
Quick Answer: What are cardiac glycosides?
Cardiac glycosides are heart medicines, such as digoxin, that make the heart muscle contract more strongly and slow a fast heart rate. They treat heart failure, atrial fibrillation and atrial flutter, usually when first-choice drugs have not worked. Because the helpful dose sits close to a harmful one, people take low doses with periodic blood checks. [1]
What the research says
Digoxin did not change survival but cut heart failure hospital stays. In a trial of 6,800 people with heart failure, deaths were almost identical (34.8% with digoxin vs 35.1% with placebo), but fewer people were hospitalized for worsening heart failure (26.8% vs 34.7%) (Digitalis Investigation Group, N Engl J Med, 1997).
Across 52 studies, digoxin had a neutral effect on death in randomized trials. A review of 621,845 patients found no change in death risk in randomized trials (risk ratio 0.99) and a small 8% drop in all-cause hospital admissions (risk ratio 0.92) (Ziff et al., BMJ, 2015).
Low-dose digoxin matched a beta-blocker on quality of life, with fewer side effects. In 160 people aged 60 or older with permanent atrial fibrillation and heart failure symptoms, quality of life at 6 months was similar, but 25% of the digoxin group had at least one adverse event vs 64% of the beta-blocker group (Kotecha et al., JAMA, 2020).
Key takeaways
Cardiac glycosides help the heart squeeze harder and beat more slowly.
Digoxin is the most commonly prescribed cardiac glycoside.
They are not a first-choice treatment anymore. Doctors usually try safer medicines first.
The safe dose and the harmful dose are close together, so low doses and blood checks matter.
Low potassium raises the risk of side effects.
It can take a few weeks to a few months to feel better.
Cardiac glycosides at a glance
Question | Short answer |
What are they? | Heart medicines that strengthen contractions and slow the heart rate |
Main example | Digoxin (brand names Cardoxin® and Lanoxin®) |
What they treat | Heart failure, atrial fibrillation, atrial flutter |
First-choice treatment? | No. Used when other heart medicines haven't worked well enough |
How taken | Tablet, liquid or capsule, usually once a day at the same time |
Time to work | A few weeks to a few months |
Biggest risk | Too much medicine in the body (toxicity), especially with low potassium |
Monitoring | Occasional blood tests to check the drug level |
What are cardiac glycosides?
Cardiac glycosides are medicines that help people with certain heart conditions by making the heart pump more strongly and more slowly.
You take them as a tablet, liquid or capsule. Most people take a dose once a day, at the same time each day.
Their name comes from the digitalis plant, also called foxglove. This plant is the original source of the best-known drugs in this group.
How do cardiac glycosides work?
Cardiac glycosides work by holding back the pump that moves sodium out of heart cells, which leads to stronger heartbeats.
Here is the chain of events, step by step:
The sodium pump slows down. The medicine blocks cell membranes from pushing sodium out.
Sodium stays inside the cells. More sodium remains in the heart muscle cells.
Calcium builds up. Extra sodium lets more calcium collect inside the cells.
The heart squeezes harder. When the cells release that calcium, the heart muscle contracts more strongly.
More blood moves with each beat. This raises the stroke volume, the amount of blood pumped per heartbeat. It can also raise the total amount of blood the heart pumps, called cardiac output.
Stronger contractions and better cardiac output help people with heart failure.
These medicines have a second effect, too. They slow electrical signals in the atrioventricular (AV) node, the part of the heart's wiring that controls your heartbeat. This slows your heart rate. A slower rate helps people with heart failure, especially if they also have a rhythm problem such as atrial fibrillation.
What are examples of cardiac glycosides?
The main examples of cardiac glycosides are digoxin, digitalis and digitoxin, with digoxin being the most commonly prescribed.
Cardiac glycoside | Notes |
Digoxin | Most commonly prescribed; brand names include Cardoxin® and Lanoxin® |
Digitalis | Named after the foxglove plant the group comes from |
Digitoxin | A related drug from the same plant family |
Oleandrin, bufalin, ouabain | Other cardiac glycoside compounds |
For detailed drug information, see this digoxin medicine guide.
What do cardiac glycosides treat?
Cardiac glycosides treat heart failure and certain fast heart rhythms, mainly atrial fibrillation and atrial flutter.
Condition | How the medicine helps | History of use |
Stronger contractions and better cardiac output | Digoxin has been used for about 200 years | |
Slows a heart rate that is too fast | Digoxin has been used for more than 50 years | |
Slows a heart rate that is too fast | — |
Which cardiac glycoside is used for heart failure?
Digoxin is the cardiac glycoside doctors prescribe for heart failure, especially when a person also has atrial fibrillation. It is not the first-line treatment for heart failure on its own.
Are cardiac glycosides being studied for cancer?
Cardiac glycosides are being studied as a possible way to stop several types of cancer cells from multiplying. This work is still at the research stage. If it proves successful, it could lead to new treatments for many people.
Who needs cardiac glycosides?
People with heart failure or certain heart arrhythmias may need cardiac glycosides when the medicines they tried first did not work well enough.
Cardiac glycosides are no longer a first-choice medicine. Newer drugs with milder side effects have replaced them as the starting treatment. Doctors prescribe them much less often than they did 30 years ago.
Medicines your doctor will usually try first include:
Beta-blockers
ACE inhibitors
Diuretics
ARBs (angiotensin II receptor blockers)
Even so, cardiac glycosides still have an important place. For some people, the benefit is worth the risk. An estimated 30% of people worldwide who have atrial fibrillation take this type of medicine.
What are the benefits of cardiac glycosides?
The main benefits of cardiac glycosides are better cardiac output in heart failure and a slower heart rate when the heartbeat is too fast.
People taking these medicines may notice:
Symptom relief. Symptoms may improve.
Better pumping. The heart moves more blood with each beat.
Rate control. A racing heartbeat slows to a safer pace.
Fewer hospital stays. The medicine may lower hospital visits for atrial fibrillation, heart failure or both.
What are the side effects of cardiac glycosides?
The common side effects of cardiac glycosides are blurry vision, headache, lightheadedness, rash, sleepiness and abnormal heart rhythms.
Side effect | What it may feel like |
Blurry vision | Things look out of focus |
Headache | Head pain or pressure |
Lightheadedness | Feeling faint or dizzy |
Rash | Skin changes or redness |
Sleepiness | Feeling unusually tired or drowsy |
Abnormal heart rhythms | Skipped, fast or irregular heartbeats |
Why do side effects happen so easily?
Side effects happen easily because the amount of cardiac glycoside that causes problems is not much higher than the amount that treats you. Doctors call this a narrow safety margin.
Two things raise the risk further:
Low potassium. Side effects are more likely when your blood potassium is low. Learn more about low potassium (hypokalemia).
Build-up in the body. These drugs stay in your body for a while, so they can accumulate over time. Kidney problems, dehydration and some other medicines, such as amiodarone, verapamil and certain antibiotics, can also raise digoxin levels.
That is why people on long-term treatment usually take a low dose. Your doctor may also check your blood from time to time. The goal is a dose that works without causing side effects.
What is cardiac glycoside toxicity?
Cardiac glycoside toxicity is what happens when too much of the medicine builds up in your body, which can cause dangerous heart rhythms.
Signs of toxicity include:
Abnormal heart rhythms, which can be fatal
Sleepiness
Vision changes, such as seeing a yellow or green tint
Upset stomach
The good news: toxicity is treatable. Doctors use fluids, electrolytes and medicines to manage it. Clinicians can find more detail in this clinical review of digoxin.
How long do cardiac glycosides take to work?
Cardiac glycosides can take a few weeks or even a few months to help you feel better.
Keep taking your medicine, even once you start to feel better.
How can you take cardiac glycosides safely?
You can take cardiac glycosides safely by sticking to your prescribed low dose and staying in close touch with your doctor.
Take it at the same time every day. Most people take one dose daily.
Don't stop on your own. Keep going even if you feel better.
Go to your blood tests. They show whether the amount of drug in your blood is right.
Report how you feel. Tell your doctor how the medicine is affecting you.
Know the warning signs. Learn the toxicity signs listed above.
When should you call a doctor while taking cardiac glycosides?
You should contact your doctor right away if you develop trouble breathing, swelling, or stomach symptoms while taking cardiac glycosides. Get emergency help for a very slow, fast or irregular heartbeat, fainting, confusion, or vision changes such as a yellow or green tint.
Call your provider right away if you have:
Trouble breathing
Swelling in your feet or hands
Upset stomach
Diarrhea
Loss of appetite
To learn more about a racing or skipping heartbeat, see our guide to heart palpitations.
Conclusion
Cardiac glycosides, led by digoxin, are some of the oldest heart medicines still in use. They help the heart pump more strongly and slow a racing heartbeat, which is why they still help many people with heart failure and atrial fibrillation.
They are not a first-choice drug, and the dose needs care. With a low dose, regular check-ins and a clear eye on the warning signs, they can be a safe and useful part of treatment.
Your next step: Save or print this guide and bring it to your next appointment. Ask your doctor whether a cardiac glycoside fits your treatment plan, how often your blood should be checked, and what your potassium level is. For the bigger picture, read our complete heart health guide.
Frequently asked questions
What is the most common cardiac glycoside?
Digoxin is the most commonly prescribed cardiac glycoside. Brand names include Cardoxin® and Lanoxin®.
Are cardiac glycosides the same as digoxin?
No. Digoxin is one cardiac glycoside. The group also includes digitalis, digitoxin, oleandrin, bufalin and ouabain.
Why aren't cardiac glycosides a first-line treatment?
Because of the risk of overdose. Beta-blockers, ACE inhibitors, diuretics and ARBs are safer and have milder side effects, so doctors usually try them first.
Where do cardiac glycosides come from?
They come from the digitalis plant, also known as foxglove, which gives the group its name.
What does yellow or green vision mean on digoxin?
Seeing a yellow or green tint can be a sign of cardiac glycoside toxicity. Contact your doctor right away.
Why does potassium matter with cardiac glycosides?
Low potassium makes side effects more likely. Your doctor may check your potassium along with your drug level.
How long does digoxin take to work?
It can take a few weeks to a few months before you feel better.
Can cardiac glycoside toxicity be treated?
Yes. Doctors treat toxicity with fluids, electrolytes and medicines.
Can I stop taking a cardiac glycoside when I feel better?
No. Keep taking it as prescribed, even if you feel better, and talk to your doctor before making any change.
Will I need blood tests while taking a cardiac glycoside?
Yes. Your doctor may check your blood for the medicine level, potassium and kidney function, because the safe dose and the harmful dose are close together.
Related Reading
Digoxin: Uses, Normal Levels and Toxicity explains how digoxin is used, dosed and monitored safely.
Heart Failure Medications: Types, Benefits, Side Effects, and How to Take Them Safely compares the main medicines used to treat heart failure.
Atrial Fibrillation (AFib): Symptoms, Causes & Treatment Guide covers AFib symptoms, stroke risk and treatment options.
Hypokalemia: A Comprehensive Guide to Managing Low Potassium Levels explains low potassium causes, symptoms and treatment.
References
Cleveland Clinic. Cardiac Glycosides: Types and What They Treat. Cleveland Clinic. Last updated December 8, 2022. https://my.clevelandclinic.org/health/treatments/24512-cardiac-glycosides
Digitalis Investigation Group. The effect of digoxin on mortality and morbidity in patients with heart failure. N Engl J Med. 1997;336(8):525-533. PMID 9036306. https://doi.org/10.1056/NEJM199702203360801
Ziff OJ, Lane DA, Samra M, et al. Safety and efficacy of digoxin: systematic review and meta-analysis of observational and controlled trial data. BMJ. 2015;351:h4451. PMID 26321114. https://doi.org/10.1136/bmj.h4451
Kotecha D, Bunting KV, Gill SK, et al. Effect of Digoxin vs Bisoprolol for Heart Rate Control in Atrial Fibrillation on Patient-Reported Quality of Life: The RATE-AF Randomized Clinical Trial. JAMA. 2020;324(24):2497-2508. PMID 33351042. https://doi.org/10.1001/jama.2020.23138
American Society of Health-System Pharmacists. Digoxin. MedlinePlus. Last revised June 15, 2017. https://medlineplus.gov/druginfo/meds/a682301.html
David MNV, Shetty M. Digoxin. StatPearls (NCBI Bookshelf). Last updated November 25, 2024. https://www.ncbi.nlm.nih.gov/books/NBK556025/
Medical disclaimer
This article is for education only and does not replace advice from your doctor. Never start, stop or change a heart medicine without talking to your healthcare provider. If you have chest pain, severe trouble breathing or fainting, call your local emergency number.
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