---
title: Aortopulmonary window
description: What an aortopulmonary window is, why it is dangerous for a baby, how it is found, when and how it is closed and when to call an ambulance.
type: disease
aliases:
  - Aortopulmonary septal defect
  - APSD
  - Aortopulmonary fistula
sources:
  - tier: guideline
    org: minzdrav-rf
    title: Дефект аортолегочной перегородки
    year: 2025
    url: https://cr.minzdrav.gov.ru/view-cr/730_2
  - tier: reference
    org: msd-manuals
    title: Aortopulmonary Window
    year: 2025
    url: https://www.msdmanuals.com/professional/pediatrics/congenital-cardiovascular-anomalies/aortopulmonary-window
  - tier: reference
    org: msd-manuals
    title: Aortopulmonary Window (MSD Manual Consumer Version)
    year: 2025
    url: https://www.msdmanuals.com/home/children-s-health-issues/birth-defects-of-the-heart/aortopulmonary-window
  - tier: reference
    org: msd-manuals
    title: Overview of Heart Defects (MSD Manual Consumer Version)
    year: 2026
    url: https://www.msdmanuals.com/home/children-s-health-issues/birth-defects-of-the-heart/overview-of-heart-defects
sources_checked: 2026-10-13
review: null
---

An aortopulmonary window, or aortopulmonary septal defect (APSD), is a congenital heart defect in which there is an opening, a "window", between adjacent parts of the ascending <Structure id="aorta">aorta</Structure> and the <Structure id="pulmonary-trunk">pulmonary trunk</Structure>.<Cite n={1} /> The aorta and the pulmonary artery still have two separate valves, as normal.<Cite n={1} /> Through the window, blood from the aorta flows directly into the lungs.<Cite n={3} />

It is a very rare defect; it may occur on its own or together with other heart defects.<Cite n={[2, 3]} /> The window itself does not close, and the damage to the lung vessels develops faster and is more severe than with the more common septal defects of the heart, so surgery is needed early, in infancy.<Cite n={1} />

<Diagram name="aortopulmonary-window">
  <p slot="normal">
    Normally the aorta and the pulmonary artery are two separate vessels, each with its own valve:
    the aorta carries blood to the organs of the body and the pulmonary artery carries it to the
    lungs.<Cite n={1} /> After birth these vessels are not directly connected, and the pressure in
    the aorta is much higher than in the pulmonary artery.<Cite n={1} />
  </p>
  <p slot="disease">
    The diagram shows one of the variants of the defect, the most common one (type I): a window in
    the wall between the aorta and the pulmonary artery just above the valves.<Cite n={1} /> With
    each heartbeat some of the blood from the aorta flows through the window into the pulmonary
    artery, and too much blood goes to the lungs.<Cite n={[1, 3]} /> The pulmonary artery and the
    left side of the heart are overloaded with the extra blood and become enlarged.<Cite n={[1, 2]} /> The diagram shows an isolated defect: the aortic and
    pulmonary valves are separate, and the ventricular septum is intact.<Cite n={1} />
  </p>
</Diagram>

## Why it happens

<Patient>

In the unborn baby, a single large vessel first leaves the heart and later divides into the pulmonary artery and the aorta. If it does not divide completely, a window remains between them.<Cite n={[1, 3]} /> The vessels divide in the 4th–5th week of pregnancy.<Cite n={1} /> The exact causes of the defect are unknown; unlike many other heart defects, it is almost never part of a chromosomal syndrome.<Cite n={1} />

The pressure in the aorta is higher than in the pulmonary artery, so with each heartbeat some of the blood from the aorta flows through the window into the pulmonary artery: this is a "left-to-right" shunt.<Cite n={1} /> Blood flows through the window both when the heart contracts and when it relaxes, as with a [patent ductus arteriosus](../patent-ductus-arteriosus/).<Cite n={[1, 2]} /> The extra blood passes through the lungs and returns to the left side of the heart, which is overloaded and becomes enlarged.<Cite n={[1, 3]} />

Right after birth the shunt may be small. In the first months of life the resistance of the lung vessels falls, and more and more blood goes to the lungs.<Cite n={[1, 2]} /> A large flow of blood under high pressure leads to [pulmonary hypertension](../pulmonary-hypertension/).<Cite n={[2, 3]} /> If the window is not closed, [Eisenmenger syndrome](../eisenmenger-syndrome/) develops: the lung vessels are damaged irreversibly, and the shunt of blood reverses direction.<Cite n={[2, 4]} /> Spontaneous closure of the window has not been described.<Cite n={1} />

</Patient>

<Student>

According to the Russian Ministry of Health guideline, APSD is a defect with a communication between adjacent parts of the ascending aorta and the pulmonary trunk in the presence of two separately formed semilunar valves; its synonyms are aortopulmonary window and aortopulmonary fistula.<Cite n={1} /> The defect results from incomplete division of the truncus arteriosus during embryonic development.<Cite n={2} /> The absence of a ventricular septal defect and the separate aortic and pulmonary artery (PA) valves distinguish it from type I–II [truncus arteriosus](../truncus-arteriosus/).<Cite n={1} />

The Russian Ministry of Health guideline distinguishes four types by location: I, proximal (directly above or a few millimetres above the semilunar valves); II, distal (in the upper part of the ascending aorta); III, complete, or total; IV, intermediate.<Cite n={1} /> According to the Russian Ministry of Health guideline, about 90% of defects are non-restrictive (large), and about the same proportion are type I.<Cite n={1} />

Data on frequency differ. According to the Russian Ministry of Health guideline, APSD accounts for 0.2–0.3% of congenital heart defects, or 0.1% according to other data<Cite n={1} />; according to the MSD Manual for professionals, less than 0.6% of all congenital cardiac malformations.<Cite n={2} /> According to the Russian Ministry of Health guideline, associated anomalies and defects occur in more than 50% of cases: transposition of the great arteries, tetralogy of Fallot, septal defects, partial anomalous pulmonary venous drainage and a right aortic arch; a rare but typical association is anomalous origin of the right coronary artery from the PA trunk.<Cite n={1} />

The shunt from the aorta to the PA occurs in both systole and diastole; the PA, left atrium and left ventricle are volume-overloaded and dilate.<Cite n={1} /> Some degree of pulmonary hypertension (PH) is almost always present; with a large defect, PA pressure is at systemic level.<Cite n={2} />

</Student>

<HeartModel highlight={['aorta', 'pulmonary-trunk']} />

The 3D model shows a normal heart; in this defect the opening is in the wall between the ascending aorta and the pulmonary trunk.<Cite n={1} />

## Symptoms

<Patient>

A large shunt leads to [heart failure](../heart-failure/).<Cite n={[2, 3]} /> In a baby it shows as fast breathing, poor feeding, tiring quickly and heavy sweating; the baby gains weight poorly.<Cite n={3} /> These children often have respiratory infections and pneumonia.<Cite n={[2, 3]} /> Heart failure may develop as early as the first weeks or even days after birth.<Cite n={1} />

Children with a small window may have no symptoms, but it is rare for this defect to cause no symptoms at all.<Cite n={1} />

A deceptive improvement is dangerous. As the pressure in the lung vessels rises, the child may get ill less often and seem better, but this improvement is false, and the time for surgery may be lost.<Cite n={1} /> In Eisenmenger syndrome, a bluish tinge appears on the skin and mucous membranes.<Cite n={1} />

</Patient>

<Student>

Examination usually reveals a parasternal heave due to right ventricular overload, a loud single second heart sound due to PH and increased peripheral pulses.<Cite n={2} /> A small defect may produce a murmur typical of a patent ductus arteriosus.<Cite n={2} /> A large shunt reduces lung compliance and increases airway resistance; this presents as dyspnoea and signs of increased work of breathing: nasal flaring, grunting and chest retractions.<Cite n={2} />

</Student>

## How it is diagnosed

<Patient>

In most babies with this defect, the doctor hears a heart murmur.<Cite n={3} /> But the diagnosis cannot be made by listening to the heart alone: there is no murmur characteristic of this defect.<Cite n={1} />

The main test is a heart ultrasound (echocardiography) with Doppler. It shows the opening between the aorta and the pulmonary artery, its size and location and the direction of the blood shunt.<Cite n={[1, 2]} /> The doctor always checks that the aorta and the pulmonary artery have two separate valves: this rules out truncus arteriosus.<Cite n={1} /> A window located higher above the valves may be hard to see on ultrasound; CT or MRI then shows the defect precisely.<Cite n={[1, 2]} />

An ECG and a chest X-ray are also done: they show overload of the chambers of the heart, its shape and the state of the lung vessels.<Cite n={[1, 3]} /> If the child is older than 6 months and ultrasound shows raised pressure in the pulmonary artery, the resistance of the lung vessels is measured through a catheter, including when Eisenmenger syndrome is suspected.<Cite n={1} />

</Patient>

<Student>

The echocardiographic sign of APSD is a dropout of the echo signal in the septum between the aorta and the PA, with a shunt across it; echocardiography is of limited value for distal defects (types II and IV).<Cite n={1} />

ECG according to the Russian Ministry of Health guideline: with non-restrictive defects, signs of left ventricular (LV) hypertrophy and overload, sometimes of the left atrium, and with PH, of right ventricular (RV) hypertrophy<Cite n={1} />; according to the MSD Manual for professionals, RV or biventricular hypertrophy.<Cite n={2} /> The chest X-ray shows cardiomegaly, a prominent main PA segment and increased pulmonary vascular markings.<Cite n={2} />

</Student>

## How it is treated

<Patient>

The defect is treated by closing the window; the main method is surgery.<Cite n={[1, 3]} /> According to the MSD Manual for professionals, surgery should be done as soon as possible after diagnosis.<Cite n={2} /> The Russian Ministry of Health guideline also describes surgery in infancy: if the signs of heart failure and pulmonary hypertension are not getting worse and the baby gains weight normally, at about 3 months, and earlier if treatment does not help.<Cite n={1} /> Heart failure medicines often cannot keep the condition under control, and if the child is not getting better, surgery must not be put off.<Cite n={1} />

Most often the window is closed with a patch.<Cite n={1} /> The surgeon decides how to operate, with or without a heart-lung machine.<Cite n={1} /> If there are other heart defects, the Russian Ministry of Health guideline advises repairing them in the same operation.<Cite n={1} /> Closing the window through a catheter with a special device (an occluder) is possible only in rare cases, when the defect is small and located far from the valves; in children open surgery is usually chosen.<Cite n={[1, 2]} /> If Eisenmenger syndrome has already developed, closing the defect is not recommended.<Cite n={1} />

After timely surgery, pulmonary hypertension usually goes away completely, and most adults who had surgery in childhood have no symptoms.<Cite n={1} /> But after surgery a residual shunt, persistent pulmonary hypertension, [aortic regurgitation](../aortic-regurgitation/) and heart rhythm problems are possible.<Cite n={1} /> That is why follow-up by a cardiologist is needed: according to the Russian Ministry of Health guideline, 1, 3, 6 and 12 months after surgery, and if problems remain, once a year in a specialised centre.<Cite n={1} /> For 6 months after closure of the defect, the Russian Ministry of Health guideline provides for prevention of [infective endocarditis](../infective-endocarditis/) before dental treatment that injures the lining of the mouth; if a shunt of blood remains or a valve leaks, prevention may be needed for longer, even for life. Whether a particular child needs it is for the doctor to decide.<Cite n={1} />

Pregnancy after a repaired defect, with good left ventricular function and no significant pulmonary hypertension, is usually well tolerated, but in Eisenmenger syndrome pregnancy is contraindicated because of the high death rate among mothers and babies.<Cite n={1} />

</Patient>

<Student>

In typical cases the Russian Ministry of Health guideline proposes closure of an isolated APSD, surgically or by transcatheter occluder.<Cite n={1} /> A patch is the most commonly described technique; division of the vessels with suture of the ends, ligation and clipping are not recommended as routine unless the specific anatomy requires them.<Cite n={1} />

According to the Russian Ministry of Health guideline, transcatheter occluder closure is recommended in adults when the defect lies at a sufficient distance from the semilunar valves, while in children with types I–III open surgery is preferred.<Cite n={1} /> Surgical repair is not recommended in Eisenmenger syndrome and severe PH with exercise desaturation.<Cite n={1} />

</Student>

## When to call an ambulance

Heart failure or cyanosis in the first week of life is a medical emergency.<Cite n={4} /> With this defect, severe heart failure may develop as early as the first days or weeks after birth, and a childhood infection or even a common cold can lead to a serious condition.<Cite n={1} />

Call your local emergency number (112 in the EU, 911 in the US and Canada, 999 in the UK) if a baby's lips or skin turn blue, if the baby breathes fast and with effort or grunts while breathing, struggles for breath during feeds and cannot feed, or has become unusually irritable.<Cite n={4} />

Worsening due to progressing heart failure or heart rhythm problems, as well as infective endocarditis, are reasons for emergency admission to hospital.<Cite n={1} /> As with any heart condition, call an ambulance for fainting, chest pain or severe shortness of breath: this is the site's general safety rule, repeated at the bottom of every page.

<Quiz />