---
title: Cor triatriatum
description: What cor triatriatum is, why a membrane in the left atrium hinders the flow of blood from the lungs, how the defect is found, how surgery corrects it and when urgent help is needed.
type: disease
aliases:
  - Cor triatriatum sinister
  - Left-sided cor triatriatum
  - Triatrial heart
sources:
  - tier: guideline
    org: minzdrav-rf
    title: Трехпредсердное сердце
    year: 2023
    url: https://cr.minzdrav.gov.ru/view-cr/772_1
  - tier: guideline
    org: esc
    title: 2020 ESC Guidelines for the management of adult congenital heart disease
    year: 2020
    doi: 10.1093/eurheartj/ehaa554
    url: https://doi.org/10.1093/eurheartj/ehaa554
sources_checked: 2026-10-14
review: null
---

Cor triatriatum is a rare congenital heart defect in which the <Structure id="left-atrium">left atrium</Structure> is divided into two chambers by a partition, a membrane.<Cite n={1} /> The <Structure id="pulmonary-veins">pulmonary veins</Structure> drain into the upper chamber, and the lower chamber connects to the <Structure id="mitral-valve">mitral valve</Structure>; usually the two chambers communicate through one or more narrow openings in the membrane.<Cite n={1} />

If there are no other defects, the membrane hinders the outflow of blood from the lungs in the same way as a narrowed valve does in [mitral stenosis](../mitral-stenosis/); the narrower the opening, the more severe the disturbance.<Cite n={1} /> The main treatment is an operation to remove the membrane.<Cite n={1} />

<Diagram name="cor-triatriatum">
  <p slot="normal">
    Normally the left atrium is a single chamber: the pulmonary veins drain into it, and from it blood
    passes through the mitral valve into the left ventricle.
  </p>
  <p slot="disease">
    In cor triatriatum a membrane divides the left atrium into two chambers.<Cite n={1} />
    The pulmonary veins drain into the upper chamber, and blood passes into the lower chamber,
    which connects to the mitral valve, through a narrow opening in the membrane.<Cite n={1} /> The
    diagram shows the isolated form of the defect: the obstruction to blood flow is the membrane
    inside the atrium, not the mitral valve.<Cite n={1} />
    The pressure in the upper chamber is high, but the pulmonary veins are not dilated.<Cite n={1} />
  </p>
</Diagram>

## Why it happens

<Patient>

The defect forms before birth: when the pulmonary veins develop abnormally in the fetus, a partition forms in the left atrium.<Cite n={1} /> Any influence that disturbs the development of the fetus can lead to the defect, whether physical, chemical, infectious or toxic.<Cite n={1} /> Whether it is inherited is unknown: there is no evidence either for or against it.<Cite n={1} />

It is a rare defect: according to the Russian Ministry of Health guideline, it accounts for about 0.1–0.4% of all congenital heart defects.<Cite n={1} />

Most often the upper chamber communicates with the lower one through an opening in the membrane.<Cite n={1} /> Less often there is no such communication, and blood from the upper chamber goes to the <Structure id="right-atrium">right atrium</Structure>, either through an [atrial septal defect](../atrial-septal-defect/) or through abnormally draining veins.<Cite n={1} /> When cor triatriatum comes with other defects, the most common is anomalous pulmonary venous drainage, either [partial](../partial-anomalous-pulmonary-venous-return/) or [total](../total-anomalous-pulmonary-venous-return/).<Cite n={1} /> Atrial and ventricular septal defects, coarctation of the aorta, tetralogy of Fallot and other defects also occur.<Cite n={1} />

</Patient>

<Student>

The membrane is fibrous or fibromuscular, usually thick, with a tubular opening; it may contain calcifications.<Cite n={1} /> It divides the left atrium (LA) into an upper (posterosuperior) proximal chamber, the common pulmonary venous chamber into which the pulmonary veins open, and a lower (anteroinferior) distal chamber, which communicates with the LA appendage and the mitral valve (MV).<Cite n={1} />

The right ventricle is usually enlarged, but the degree of enlargement depends on the left-to-right shunt at atrial level; the left ventricle (LV) is of normal size or moderately hypoplastic.<Cite n={1} />

The 2020 ESC guidelines on adult congenital heart disease list cor triatriatum in the table of [pulmonary hypertension](../pulmonary-hypertension/) subtypes, among the clinical settings of isolated post-capillary pulmonary hypertension, next to pulmonary vein obstruction and systemic ventricular or systemic atrioventricular valve dysfunction; they contain no specific recommendations for this defect.<Cite n={2} />

The term cor triatriatum dexter is used for various anomalies with division of the right atrium; it is not related to classic (left-sided) cor triatriatum.<Cite n={1} />

</Student>

<HeartModel highlight={['left-atrium', 'pulmonary-veins', 'mitral-valve', 'interatrial-septum']} />

The 3D model shows a normal heart, with no membrane in it. The highlighting marks where the membrane lies in this defect: inside the left atrium, between the openings of the pulmonary veins and the mitral valve; one of its edges arises from the <Structure id="interatrial-septum">wall between the atria</Structure>.<Cite n={1} />

## Symptoms

<Patient>

The defect shows itself in very different ways: it depends on how narrow the opening in the membrane is and on the shunting of blood through an opening between the atria, if there is one.<Cite n={1} />

If the opening is very narrow, blue-tinged skin (cyanosis), breathlessness, a cough and crackles in the lungs appear in the first days of life and get worse; [heart failure](../heart-failure/) then develops, and the child falls behind in physical development.<Cite n={1} /> The child may have difficulty feeding, gain weight poorly, and have an enlarged liver and swelling of the face and legs.<Cite n={1} /> Such children are often treated for pneumonia, and the defect is found only on a heart ultrasound.<Cite n={1} />

If the opening is wider, the symptoms build up more slowly.<Cite n={1} /> Very rarely the defect is first found in adults: this happens when the membrane obstructs blood flow less.<Cite n={1} /> The doctor asks about breathlessness, palpitations, whether exercise has become harder, poor weight gain and frequent chest infections.<Cite n={1} />

</Patient>

<Student>

Cyanosis of the skin and visible mucous membranes is due to communication between the atria through the foramen ovale or an atrial septal defect.<Cite n={1} /> The auscultatory findings are non-specific and in some cases may be entirely absent; when pulmonary hypertension develops, the second heart sound is accentuated over the pulmonary artery.<Cite n={1} /> Unlike patients with mitral stenosis, patients with cor triatriatum have no history of rheumatic fever.<Cite n={1} />

</Student>

## How it is diagnosed

<Patient>

The main test is a heart ultrasound ([echocardiography](../../diagnostic/echocardiography/)) with colour Doppler mapping.<Cite n={1} /> It shows where the membrane lies, whether it has an opening and how large it is, where the pulmonary veins drain and whether there is an opening between the atria.<Cite n={1} /> In difficult cases, transoesophageal echocardiography is done: it shows the membrane well and makes it possible to assess how much it obstructs the outflow of blood from the lungs.<Cite n={1} />

The [ECG](../../diagnostic/ecg/) shows no specific signs of the defect.<Cite n={1} /> A chest X-ray shows enlargement of the right side of the heart and increased venous markings in the lungs, sometimes a picture of pulmonary oedema.<Cite n={1} /> If the ultrasound findings are inconclusive, a contrast-enhanced cardiac CT scan is done before surgery; cardiac MRI is recommended for adults.<Cite n={1} /> If the ultrasound shows raised pressure in the pulmonary artery, cardiac catheterisation is performed.<Cite n={1} />

</Patient>

<Student>

In the parasternal long-axis view of the LV, a fixed linear echo extends from the free wall of the LA to the interatrial septum; in the apical four-chamber view its presence is confirmed and an artefact is excluded.<Cite n={1} /> Low-velocity phasic flow with a peak velocity below 1 m/s indicates no obstruction; coexisting MV stenosis can mask moderate obstruction at the level of the membrane, so the morphology of the MV and subvalvular apparatus is examined.<Cite n={1} />

The ECG shows right axis deviation in most cases.<Cite n={1} /> At catheterisation, a reliable sign of the defect is two areas with different pressures in the LA.<Cite n={1} />

</Student>

## How it is treated

<Patient>

Before surgery, medicines such as diuretics reduce congestion of blood in the lungs and help stabilise the patient's condition; this is temporary treatment until the operation, and it does not replace it.<Cite n={1} /> If an adult has heart failure, or it persists after the operation, it is treated in the same way as heart failure from other causes.<Cite n={1} /> Which medicines are needed and for how long is decided by the doctor.

The definitive treatment is surgery: the surgeon removes the membrane that obstructs blood flow inside the left atrium.<Cite n={1} /> Surgery is recommended if the opening in the membrane is narrow, for adults with symptoms of the defect, and when it occurs together with other congenital heart defects.<Cite n={1} /> The membrane itself is not an absolute indication for surgery: if the opening is wide, surgery is done when the defect limits the ability to work or contributes to other diseases.<Cite n={1} />

When the condition is very severe, most often in young children, the operation becomes an emergency, the only way to save the patient's life.<Cite n={1} /> In a critical condition the opening may be widened as an emergency with a balloon passed through the blood vessels; this can be life-saving and makes it possible to bring the patient out of the critical condition.<Cite n={1} />

After timely surgery the outlook is good; life expectancy and physical capacity may be limited if there is pulmonary hypertension.<Cite n={1} /> After the operation the opening may narrow again, pulmonary hypertension may persist and heart rhythm problems can occur, so regular follow-up with a cardiologist, with an ECG and heart ultrasound, is needed.<Cite n={1} /> After the operation, the doctor may prescribe prevention of [endocarditis](../infective-endocarditis/) before dental procedures that damage the lining of the mouth.<Cite n={1} />

</Patient>

<Student>

According to the Russian Ministry of Health guideline, surgical treatment is indicated for a restrictive opening between the proximal and distal chambers, for adults with clinical manifestations, for associated congenital heart defects, and for atypical forms with a severe course, for example when the common pulmonary venous chamber opens into the right atrium; these recommendations have grade of recommendation C.<Cite n={1} />

Conservative treatment is used to stabilise the patient before surgery: diuretics, inotropes for low cardiac output, and ECMO for neonates with a restrictive communication, low cardiac output and severe hypoxaemia; emergency balloon dilatation is performed with the double-balloon technique.<Cite n={1} /> Heart failure is the most common problem in adults with cor triatriatum or after its repair; it is treated according to the general guidelines.<Cite n={1} />

</Student>

## When to call an ambulance

With a very narrow opening, the defect shows itself in the first days of life, and a very severe condition needs emergency surgery.<Cite n={1} /> If a baby's lips and skin are becoming increasingly blue, or breathlessness is getting worse, especially if it makes feeding difficult, call your local emergency number (112 in the EU, 911 in the US and Canada, 999 in the UK).<Cite n={1} /> The Russian Ministry of Health guideline names as reasons for emergency hospital admission a deterioration due to worsening heart failure or rhythm disturbances, acute heart rhythm disturbances, and infective endocarditis.<Cite n={1} /> As with any heart condition, call an ambulance for fainting, chest pain or severe breathlessness: this is the site's general safety rule, repeated at the bottom of every page.

<Quiz />