---
title: Congenital subaortic stenosis
description: What congenital subaortic stenosis is, why an obstruction to blood flow forms below the aortic valve, how the defect is found, how it is treated and when urgent help is needed.
type: disease
aliases:
  - Subaortic stenosis
  - Subvalvular aortic stenosis
  - Subaortic membrane
  - Discrete subaortic stenosis
  - SubAS
sources:
  - tier: guideline
    org: minzdrav-rf
    title: Врожденный подклапанный стеноз аорты
    year: 2025
    url: https://cr.minzdrav.gov.ru/view-cr/745_2
  - 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
  - tier: reference
    org: msd-manuals
    title: Aortic Stenosis
    year: 2025
    url: https://www.msdmanuals.com/professional/cardiovascular-disorders/valvular-disorders/aortic-stenosis
  - tier: reference
    org: msd-manuals
    title: Hypertrophic Cardiomyopathy
    year: 2026
    url: https://www.msdmanuals.com/professional/cardiovascular-disorders/cardiomyopathies/hypertrophic-cardiomyopathy
sources_checked: 2026-10-14
review: null
---

Congenital subaortic stenosis is a heart defect in which the obstruction to blood flow lies not in the <Structure id="aortic-valve">aortic valve</Structure> itself but below it, where blood leaves the <Structure id="left-ventricle">left ventricle</Structure> for the <Structure id="aorta">aorta</Structure>.<Cite n={[1, 2]} /> It may be a fibrous membrane or ring just below the valve, or a longer fibromuscular narrowing.<Cite n={[1, 2, 3]} /> When the valve itself is narrowed, that is a different disease: [aortic stenosis](../aortic-stenosis/).<Cite n={3} />

The Russian Ministry of Health guideline on this defect is written for children, and the European Society of Cardiology (ESC) guideline for adults with congenital heart disease, so the text says which source says what. The defect is treated with surgery.<Cite n={[1, 2]} />

<Diagram name="subaortic-stenosis">
  <p slot="normal">
    The diagram shows systole, when the left ventricle contracts. Normally blood leaves the left
    ventricle for the aorta through the open aortic valve, and nothing gets in its way below the
    valve.<Cite n={3} />
  </p>
  <p slot="disease">
    In subaortic stenosis the outflow of the left ventricle is narrowed by a membrane lying just
    below the aortic valve or a little lower; in the diagram the valve itself is
    ordinary.<Cite n={[1, 2]} /> Blood passes through the narrow opening in the membrane as a fast
    jet, which damages the aortic valve.<Cite n={1} /> So over time the valve often starts to leak
    blood back into the ventricle. This happens in diastole, when the valve is closed, so the
    backflow is not shown in this diagram of systole.<Cite n={[1, 2]} />
  </p>
</Diagram>

## Why it happens

<Patient>

This is a congenital defect. According to the Russian Ministry of Health paediatric guideline, it makes up 1–1.5% of all congenital heart defects and is 1.5–2 times more common in males.<Cite n={1} />

The narrowing takes different forms: a membrane with an opening, a fibrous ridge, a fibromuscular "collar" or a long narrow tunnel.<Cite n={1} /> According to the Russian Ministry of Health paediatric guideline, in children who have surgery at an early age a membrane is found most often.<Cite n={1} /> Sometimes the outflow of the ventricle is narrowed by abnormalities of the <Structure id="mitral-valve">mitral valve</Structure>.<Cite n={1} />

The defect may occur on its own, but it is often combined with others: a [bicuspid aortic valve](../bicuspid-aortic-valve/), a [ventricular septal defect](../ventricular-septal-defect/), [coarctation of the aorta](../coarctation-of-the-aorta/) or an [atrioventricular septal defect](../atrioventricular-septal-defect/).<Cite n={[1, 2]} /> It can also appear after surgery for such defects.<Cite n={[1, 2]} />

The fast jet of blood through the narrowing damages the aortic valve, and the valve may start to leak blood back: this is [aortic regurgitation](../aortic-regurgitation/).<Cite n={1} /> According to the Russian Ministry of Health paediatric guideline, in children this regurgitation often gets worse; according to the ESC, in adults it is frequent but rarely significant or progressive.<Cite n={[1, 2]} /> How fast the narrowing itself progresses differs from person to person.<Cite n={[1, 2]} />

Subaortic stenosis has to be told apart from [hypertrophic cardiomyopathy](../hypertrophic-cardiomyopathy/).<Cite n={[1, 2]} /> That is a different disease, a disease of the heart muscle itself, usually genetic; in its obstructive form the outflow of the left ventricle is narrowed by the thickened septum and the front leaflet of the mitral valve, which the blood flow pushes into the outflow.<Cite n={4} />

</Patient>

<Student>

According to the Russian Ministry of Health paediatric guideline, the substrate of subaortic stenosis may be changes in the subvalvular space or abnormalities of neighbouring structures, in particular the mitral valve.<Cite n={1} /> The V.N. Getmansky classification distinguishes membranous-diaphragmatic, ridge-like, fibromuscular and tunnel types.<Cite n={1} /> The membrane is a circular fibrous membrane with one or more openings 0.5–1.5 cm in size, or a crescent-shaped fibrous fold; it usually lies immediately below the aortic valve annulus or a little lower and may attach along the base of the anterior mitral leaflet and to the interventricular septum.<Cite n={1} /> A ridge lies 0.5–2 cm below the aortic valve and a fibromuscular "collar" 1–3 cm below it; the tunnel form is the extreme degree of the fibromuscular type, with marked hypertrophy of the LVOT muscle and a tunnel 1–3 cm long.<Cite n={1} /> The ESC describes the cause as a fibrous ridge or ring in the LVOT proximal to the aortic valve, or a fibromuscular narrowing.<Cite n={2} />

The ESC lists aortic valve disease, VSD, AVSD and Shone complex (multilevel left heart obstruction) as associated lesions.<Cite n={2} /> The Russian Ministry of Health paediatric guideline also describes subaortic stenosis forming after repair of a VSD or double outlet right ventricle: the altered LVOT geometry may produce turbulent flow that acts on the interventricular septum.<Cite n={1} />

The sources describe the rate of progression differently. According to the Russian Ministry of Health paediatric guideline, it is variable and unpredictable in children, while in adults the defect progresses slowly.<Cite n={1} /> According to the ESC (adults), the clinical course is highly variable, progression is related to associated CHD, particularly a VSD, and age seems not to play a role.<Cite n={2} />

The Russian Ministry of Health paediatric guideline notes that with marked LVH the tunnel form must be differentiated from obstructive HCM, because treatment strategy depends on it.<Cite n={1} /> In HCM the LVOT obstruction is dynamic: it results from the hypertrophied basal interventricular septum and systolic anterior motion of the mitral valve.<Cite n={[3, 4]} />

</Student>

<HeartModel highlight={['left-ventricle', 'interventricular-septum', 'aortic-valve', 'mitral-valve']} />

The 3D model shows a normal heart with no membrane: the highlight only marks the area where the narrowing occurs, the outflow of the left ventricle below the aortic valve, between the <Structure id="interventricular-septum">interventricular septum</Structure> and the front leaflet of the mitral valve.<Cite n={1} />

## Symptoms

<Patient>

The defect may cause no symptoms for a long time, even in older children and adults; according to the Russian Ministry of Health paediatric guideline, there are often no symptoms even when the narrowing is significant.<Cite n={1} /> It is often found when a child is examined because of another heart defect.<Cite n={1} /> Isolated subaortic stenosis is rare in newborns and infants, and symptoms more often appear after the age of one.<Cite n={1} />

According to the Russian Ministry of Health paediatric guideline, the main complaints are shortness of breath, tiring easily, sweating and delayed development.<Cite n={1} /> Older patients may have fainting, heart pain and congestive [heart failure](../heart-failure/); these symptoms occur with moderate or severe narrowing.<Cite n={1} />

Fainting is a bad sign: with marked narrowing, during exercise the heart pumps out less blood, blood pressure falls and the brain does not get enough blood.<Cite n={1} /> Chest pain during exercise happens because the heart muscle does not get enough blood supply when it needs more oxygen.<Cite n={1} />

Without treatment the defect can lead to thickening of the left ventricular wall, heart rhythm problems, aortic regurgitation, [infective endocarditis](../infective-endocarditis/) and sudden death.<Cite n={1} /> According to the ESC, sudden death is infrequent but has been reported.<Cite n={2} />

</Patient>

<Student>

According to the Russian Ministry of Health paediatric guideline, syncope and presyncope are rare in children and are more often caused by arrhythmias.<Cite n={1} /> Syncope is due to reduced cerebral perfusion, and heart pain to relative coronary insufficiency.<Cite n={1} /> Percussion may show the cardiac borders extended to the left because of LVH, and palpation a diffuse apex beat.<Cite n={1} />

</Student>

## How it is diagnosed

<Patient>

The doctor hears a heart murmur.<Cite n={[1, 2]} /> Unlike narrowing of the valve itself, isolated subaortic stenosis has no "ejection click", an important sign that helps tell them apart.<Cite n={[1, 2]} /> A murmur in diastole means that the aortic valve leaks blood back.<Cite n={2} />

The main test is a heart ultrasound ([echocardiography](../../diagnostic/echocardiography/)) with Doppler: it shows the outflow of the left ventricle, the aortic valve, any backflow through it, how well the left ventricle works and how thick its wall is, other defects, and how marked the narrowing is.<Cite n={[1, 2]} /> Sometimes a better view of the membrane needs transoesophageal echocardiography, in which the probe is passed into the gullet.<Cite n={[1, 2]} />

An [ECG](../../diagnostic/ecg/) may be normal when the narrowing is small, and when it is significant it shows strain and thickening of the left side of the heart.<Cite n={1} /> When the outflow of the ventricle has a complex structure, CT with contrast or MRI helps.<Cite n={[1, 2]} />

</Patient>

<Student>

Auscultation according to the Russian Ministry of Health paediatric guideline: a harsh systolic murmur loudest in the 2nd–3rd intercostal space to the right of the sternum, radiating to the carotid arteries; its duration is directly proportional to the degree of obstruction; some patients have a diastolic murmur of aortic regurgitation.<Cite n={1} /> The ESC describes in adults a systolic ejection murmur at the left sternal border without a systolic ejection click.<Cite n={2} />

The Russian Ministry of Health paediatric guideline grades severity in children by the maximum systolic pressure gradient between the LV and the aorta: minimal stenosis up to 30 mm Hg, moderate 30–50 mm Hg, severe more than 50 mm Hg.<Cite n={1} /> According to the Russian Ministry of Health paediatric guideline, children with a gradient below 50 mm Hg and shortness of breath and fatigue should have exercise echocardiography.<Cite n={1} /> According to the ESC, Doppler-derived gradients may overestimate the obstruction and may require confirmation by cardiac catheterisation.<Cite n={2} /> A hypertrophied interventricular septum may hide the membrane; transoesophageal echocardiography can distinguish subaortic stenosis from a hypertrophied septum.<Cite n={1} />

</Student>

## How it is treated

<Patient>

According to the ESC guideline for adults, surgery is the only effective treatment.<Cite n={2} /> The surgeon removes the membrane or ridge and part of the muscle below it on the septal side; the fibromuscular and tunnel forms need more extensive operations.<Cite n={[1, 2]} /> If the aortic valve leaks markedly, it is repaired or replaced during the same operation.<Cite n={[1, 2]} />

Whether and when surgery is needed is decided by the doctor, who takes into account how marked the narrowing is, symptoms (fainting, chest pain), and the state of the aortic valve and the left ventricle.<Cite n={[1, 2]} /> The thresholds differ for children (Russian Ministry of Health) and adults (ESC).<Cite n={[1, 2]} /> According to the Russian Ministry of Health paediatric guideline, children and teenagers with a small narrowing, no symptoms and no thickening of the left ventricular wall are followed up without surgery.<Cite n={1} />

After surgery there may be damage to the aortic or mitral valve, heart conduction problems (atrioventricular block) or a new hole in the wall between the ventricles.<Cite n={[1, 2]} /> The results of surgery are good, but the narrowing may come back, and aortic regurgitation may appear or get worse.<Cite n={[1, 2]} /> So follow-up by a cardiologist with regular echocardiography is needed both before and after surgery, and in adults for life.<Cite n={[1, 2]} /> According to the Russian Ministry of Health paediatric guideline, infants and young children are seen more often, every 3–6 months.<Cite n={1} />

After the valve has been replaced with a prosthesis, lifelong prevention of blood clots is needed.<Cite n={1} /> In addition, before procedures that injure the lining of the mouth or airways (for example, before a tooth extraction), prevention of endocarditis may be needed; people with a prosthetic valve and those who still have backflow through a valve after surgery may need it for a long time, sometimes for life.<Cite n={[1, 2]} /> Both are prescribed by the doctor. According to the Russian Ministry of Health paediatric guideline, children with mild narrowing have no limits on physical activity, while with moderate and severe narrowing intense and competitive exercise is not recommended.<Cite n={1} /> According to the ESC, pregnancy is contraindicated only with severe stenosis with symptoms: in that case surgery is done before pregnancy, and with severe stenosis without symptoms surgery before pregnancy should be discussed.<Cite n={2} />

</Patient>

<Student>

The Russian Ministry of Health guideline (children) recommends surgery with a peak LV–aorta gradient of 50 mm Hg or more or a mean gradient of 30 mm Hg or more, and at lower gradients with progressive moderate-to-severe AR with LV enlargement or similar MR; surgery should be considered at lower gradients with syncope and angina, with ST-segment changes and progressive LVH in asymptomatic patients, and with LVEF below 50%.<Cite n={1} /> The Russian Ministry of Health paediatric guideline regards syncope as an absolute indication for surgical repair.<Cite n={1} /> The ESC (adults) recommends surgery in symptomatic patients with a mean Doppler gradient of 40 mm Hg or more or severe AR (I C); in asymptomatic patients it should be considered, for example, with a mean gradient of 40 mm Hg or more and marked LVH or a fall in blood pressure on exercise.<Cite n={2} /> In patients with low surgical risk and anatomy well suited to repair, the threshold for intervention is lower than in aortic valve stenosis, since no valve implant is required.<Cite n={2} />

For discrete subaortic stenosis the Russian Ministry of Health paediatric guideline recommends excision of the subaortic membrane (membranectomy) or myectomy; for the tunnel form without involvement of the aortic valve and without annular hypoplasia, a modified Konno operation; and with significant AR, stenosis and hypoplasia of the aortic valve annulus, operations of the Ross-Konno and Konno-Rastan type.<Cite n={1} /> The Russian Ministry of Health paediatric guideline suggests considering balloon dilatation as an alternative to open surgery only for an isolated thin membrane no more than 3 mm thick; this recommendation rests on a single case series and has a low strength of recommendation (C). The ESC considers only surgical treatment effective.<Cite n={[1, 2]} />

The ESC recommends follow-up in specialised ACHD centres.<Cite n={2} /> After repair the Russian Ministry of Health paediatric guideline describes residual gradient, recurrent obstruction, development of AR and MR, iatrogenic VSD and third-degree AV block requiring pacemaker implantation.<Cite n={1} />

</Student>

## When to call an ambulance

Surgery for subaortic stenosis is usually planned, but with marked narrowing dangerous situations can occur.<Cite n={1} /> Call your local emergency number (112 in the EU, 911 in the US and Canada, 999 in the UK) if a person with this defect has lost consciousness or nearly lost it, especially during exercise, if chest pain has appeared during exercise, or if shortness of breath is quickly getting worse.<Cite n={1} /> A person with a prosthetic valve also needs urgent help for bleeding that cannot be stopped.<Cite n={1} /> If a raised temperature persists for no clear reason, do not put off seeing a doctor, and tell them about the heart defect or the operation: this may be how [infective endocarditis](../infective-endocarditis/) starts.<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 />