Cor Triatriatum: Symptoms, Causes, Diagnosis, Treatment and Outlook — What You Need to Know
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
Quick Answer: Cor triatriatum is a rare congenital heart defect, present at birth, in which a membrane divides one of the top heart chambers (the atria) into two sections. The name means "heart with three atria" because the membrane makes the chamber look like two on imaging. The membrane restricts blood flow, and if the opening in it is missing or very small, blood backs up in the heart, which can cause heart failure and serious complications. In babies, symptoms usually appear early as breathing trouble, poor weight gain, extreme sleepiness, a bloody cough, or swelling. Surgery is the main treatment: the membrane is removed so blood can flow normally again. Many children and adults do well after surgery, but lifelong follow-up with a cardiologist is required.
TL;DR
Cor triatriatum is a rare birth defect of the heart (roughly 1 to 4 in every 1,000 cases of congenital heart disease) where a membrane divides one of the two top heart chambers into two sections, restricting blood flow. It most often affects the left atrium. Symptoms typically appear in infancy (fast or troubled breathing, slow weight gain, extreme sleepiness, coughing up blood, and swelling) and call for prompt medical care. Surgery to remove the membrane is the main treatment and often restores normal blood flow. Most children and adults do well after surgery, but lifelong cardiology follow-up is needed.
When Should You Seek Care for a Baby?
Seek medical attention right away if your baby or child has trouble breathing or any of the symptoms listed in this article.
Keep in mind there are many possible causes for these issues, and your child doesn't necessarily have a heart defect. But if a heart defect is the cause, seeking care quickly helps them get the treatment they need.
If you notice | Action |
Trouble breathing or fast breathing | Call a healthcare provider right away |
Slower weight gain than expected | Call a healthcare provider right away |
Extreme sleepiness | Call a healthcare provider right away |
A cough that produces blood | Call a healthcare provider right away |
Swelling in legs, feet, or belly | Call a healthcare provider right away |
An adult suspecting an undiagnosed heart defect | Reach out to a healthcare provider |
What Exactly Is Cor Triatriatum?
The human heart has four chambers. The two top chambers are called atria, and they receive blood returning to the heart. Cor triatriatum is a heart defect that's present at birth (congenital), in which a membrane divides one of the top chambers into two separate sections.
This membrane makes it harder for blood to flow normally through the heart. The membrane may have an opening that lets some blood through. But if there isn't one, or if the opening is small, blood can back up in the heart. This may lead to heart failure and other complications.
The condition gets its name from what it looks like on imaging. On an echo test, cor triatriatum makes it look like the child has three atria rather than the expected two. "Cor triatriatum" is Latin for "heart with three atria."
Is cor triatriatum something a child is born with?
Yes. It is a congenital heart defect, meaning it's present at birth. The membrane forms during fetal development, before the baby is ever born.
How Does Cor Triatriatum Look on Imaging Tests?
Cor triatriatum isn't visible from the outside. It shows up on heart imaging. On an echocardiogram (echo test), the divided top chamber makes the heart look like it has three atria instead of the usual two. That characteristic appearance is how doctors recognize the condition, and it's also where the name comes from.
Other imaging (chest X-ray, heart CT scan, and heart MRI) can show the structure of the heart and check for complications.
What Are the Signs and Symptoms of Cor Triatriatum?
Symptoms usually appear in infancy or early childhood. Because blood can back up in the heart when the membrane's opening is missing or small, the signs reflect that strain on the heart and lungs.
Symptom in infants and young children | What it looks like |
Trouble breathing or fast breathing | Breathing harder or faster than normal |
Slower weight gain than expected | Not gaining weight at the expected pace |
Extreme sleepiness | Unusually sleepy, hard to rouse |
A cough that produces blood | Coughing up blood |
Swelling in legs, feet, or belly | Visible fluid buildup in the lower body or abdomen |
Can cor triatriatum cause no symptoms until adulthood?
Rarely, yes. When that happens, adult symptoms may include chest pain or discomfort, coughing up blood, fainting, heart palpitations, tiring easily, trouble breathing (especially during physical activity or when lying down), and swelling in the legs or belly. Adults are sometimes diagnosed when symptoms finally develop, or when signs show up on an imaging test that was done for another reason entirely.
What Causes Cor Triatriatum?
Changes that occur during fetal development cause cor triatriatum. These changes result in a membrane forming in one of the top heart chambers. The condition is not something parents do or don't do. It's a structural event that happens while the heart forms before birth.
Are there genetic causes of cor triatriatum?
No. Cor triatriatum has no known genetic causes, and there's no evidence that it's passed down within families.
Why does the membrane form?
Experts are still exploring exactly which changes cause the most common type, cor triatriatum sinister. A leading theory is that the common pulmonary vein doesn't merge with the left atrium as it should. With the rarer type, cor triatriatum dexter, fetal heart tissue that normally goes away on its own instead stays in place and forms the membrane.
Are other heart defects associated with cor triatriatum?
Some babies with cor triatriatum also have other heart defects.
Possible associated heart defect | What it is |
Atrial septal defect | A hole between the top heart chambers |
Total anomalous pulmonary venous return | Pulmonary veins connect to the wrong side of the heart |
Partial anomalous pulmonary venous return | Some pulmonary veins connect to the wrong side of the heart |
What Are the Types of Cor Triatriatum?
There are two main types, based on where the membrane is located.
Type | Where the membrane is | How common |
Cor triatriatum sinister | Left atrium | Most people have this type |
Cor triatriatum dexter | Right atrium | Very rare |
With cor triatriatum sinister, the membrane sits in the left atrium. One section contains the pulmonary veins, the vessels that receive blood from the lungs. The other contains the mitral valve, the "door" that sends blood down to the left ventricle.
The three severity groups of cor triatriatum sinister
Group | What the membrane looks like | What it means for blood flow |
Group 1 | No opening in the membrane at all | Blood must take a different route instead, possibly through a patent foramen ovale (a hole between the top chambers that normally closes after birth) |
Group 2 | One or more openings, but very small | It's hard for blood to flow down to the left ventricle |
Group 3 | One hole, large enough for easy passage | Blood passes through easily |
Groups 1 and 2 are more severe and cause symptoms early in life. These are the most common groups. Group 3 is milder and less common, and it usually doesn't cause symptoms until adulthood, if at all.
What Complications Can Cor Triatriatum Cause?
Cor triatriatum disrupts normal blood flow through the heart. This can lead to serious complications.
Possible complication | What it is |
Atrial arrhythmias | Abnormal heart rhythms in the top chambers |
Tricuspid regurgitation | A leaky heart valve on the right side of the heart |
Heart failure | Problems with the heart's pumping ability |
Pulmonary hypertension | Raised pressure in the pulmonary arteries |
Cardiac arrest | Sudden stopping of the heart |
Because cardiac arrest is on this list, prompt care for any symptom is especially important. Early diagnosis means early treatment, before these complications develop.
How Is Cor Triatriatum Diagnosed?
Healthcare providers diagnose cor triatriatum with a physical exam and testing. During the exam, the provider will listen to the child's heart and lungs with a stethoscope and look for visible signs of heart problems, like swelling in the belly or legs. Imaging tests then show the structure of the heart and check for complications.
Diagnostic test | What it does |
Physical exam with a stethoscope | Listens to heart and lungs; checks for visible signs like swelling |
Chest X-ray | Images the chest structure |
Echocardiogram (echo) | Ultrasound showing the divided atrium, which can make the heart look like it has three atria |
Heart CT scan | Detailed imaging of the heart's structure |
Heart MRI scan | Detailed imaging of the heart's structure and complications |
Adults can be diagnosed too, sometimes when symptoms develop, or when signs appear on an imaging test done for another reason.
How Is Cor Triatriatum Treated?
Surgery is the main treatment for cor triatriatum. In general, a surgeon removes the membrane that divides the left or right atrium. This allows blood to flow better through the heart. The surgeon may also repair other heart issues at the same time. The exact details vary based on the anatomy of the child's heart, including any other heart defects they have.
Do adults always need surgery?
Adults who are diagnosed but don't have symptoms may not need surgery right away. Healthcare providers monitor the condition and decide the best time for surgery.
What Is the Outlook After Treatment?
Your child's outlook depends on many factors, including any other heart defects they have. In general, many children and adults do well after surgery to treat cor triatriatum. Surgery can help blood flow normally through the heart and relieve symptoms.
One requirement is permanent: anyone with this condition needs routine follow-up visits with a heart doctor (cardiologist) throughout their life.
A note for parents
It can feel scary or overwhelming to learn your child has a rare heart defect. But it may help to know that cor triatriatum is treatable with surgery. Your child's care team will be there to support you throughout the process. It may also help to connect with other parents and caregivers who have children with congenital heart disease.
Conclusion: What You Should Remember
Cor triatriatum is a rare congenital heart defect, about 1 to 4 in every 1,000 cases of congenital heart disease, where a membrane divides one of the top heart chambers into two sections. Symptoms usually appear in infancy, and breathing trouble in a baby always deserves prompt medical attention. Surgery removes the membrane, restores normal blood flow, and many children and adults do well afterward. The ongoing commitment is lifelong follow-up with a cardiologist.
Next step: If your baby is breathing fast, gaining weight slowly, unusually sleepy, coughing up blood, or showing swelling, call a healthcare provider right away. If an adult reading this recognizes themselves in the symptom list, reach out to a healthcare provider about evaluation.
Frequently Asked Questions
What is cor triatriatum?
A congenital heart defect present at birth in which a membrane divides one of the top heart chambers (atria) into two separate sections, making blood flow harder.
Why is it called cor triatriatum?
On an echo test, the divided chamber makes it look like the heart has three atria instead of two. The name comes from the Latin for "heart with three atria."
Is cor triatriatum rare?
Yes. Experts estimate it accounts for 1 to 4 in every 1,000 cases of congenital heart disease.
Is cor triatriatum genetic or hereditary?
No. There are no known genetic causes, and no evidence it's passed down within families.
What is the difference between cor triatriatum sinister and dexter?
Sinister means the membrane is in the left atrium, and most people have this type. Dexter means the membrane is in the right atrium, which is very rare.
Which group of cor triatriatum is most severe?
Groups 1 and 2 are more severe, cause symptoms early in life, and are the most common. Group 3 is milder, less common, and usually causes no symptoms until adulthood.
What are the symptoms of cor triatriatum in babies?
Trouble breathing or fast breathing, slower weight gain than expected, extreme sleepiness, a cough that produces blood, and swelling in the legs, feet, or belly.
How is cor triatriatum diagnosed?
With a physical exam plus imaging tests such as a chest X-ray, echocardiogram, heart CT scan, or heart MRI.
What is the treatment for cor triatriatum?
Surgery is the main treatment. The surgeon removes the membrane dividing the atrium so blood can flow better, and may repair other heart issues at the same time.
Does everyone with cor triatriatum need surgery right away?
Adults diagnosed without symptoms may not need surgery right away. Providers monitor the condition and decide the best timing.
Is lifelong follow-up needed after treatment?
Yes. Anyone with this condition needs routine follow-up visits with a cardiologist throughout their life.
What should I do if my baby is breathing fast or gaining weight slowly?
Call a healthcare provider right away. These can be symptoms of cor triatriatum, though many other conditions can cause them too. Quick care helps either way.
Related Reading
References
1. Cleveland Clinic. Cor Triatriatum (medically reviewed; last updated May 6, 2026). https://my.clevelandclinic.org/health/diseases/cor-triatriatum
External resources: American Heart Association: Congenital Heart Defects · MedlinePlus: Congenital Heart Disease · Children's Heart Foundation · Mended Little Hearts
Disclaimer: This article is for general information only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare provider with any questions about a medical condition. Never delay seeking medical care because of something you read here. In an emergency, call your local emergency number immediately.
Comments