Embryology · Heart and vessels
Ventricular septal defect !
- Malformation
A hole in the wall between the ventricles lets blood pass from the left side to the right. It is the most common congenital heart defect.
Updated 2026-11-01
See it in 3D: Interventricular septum · Right ventricle · Left ventricle
What it is
A ventricular septal defect (VSD) is a hole in the interventricular septum through which blood shunts left to right. It is acyanotic at first, and its severity depends on size. Small defects, especially muscular ones, often close on their own; large ones cause heart failure and, untreated, pulmonary hypertension.
Embryological cause
- Perimembranous: endocardial cushion and conal ridge tissue fails to fuse with the edge of the muscular septum (week 7).
- Muscular: perforations from excess resorption of muscle as the septum grows; can be multiple ('Swiss cheese').
- Outlet (subarterial): failure of the conal septum; this is the VSD of tetralogy when the infundibular septum is malaligned.
- Inlet: part of the cushion (AV canal) defect.
Markers
- TBX5
- GATA4
- NKX2-5
- Trisomy 21
How it presents
- Newborn: often no murmur at first, because pulmonary resistance is still high.
- After a few weeks: fast breathing, sweating with feeds and poor weight gain in large VSDs.
- Harsh holosystolic murmur at the lower left sternal border, sometimes with a thrill.
- Complications: heart failure, pulmonary hypertension, endocarditis, aortic regurgitation in subarterial defects.
Diagnosis
- Doppler echocardiography confirms size, site and direction of flow.
- Prenatal: large defects may be seen on fetal ultrasound; small ones are often missed.
- Chest X-ray: cardiomegaly and increased pulmonary vascular markings in large defects.
Test yourself
Think of the answer, then tap the question to see it.
What is the most common congenital heart defect?
Ventricular septal defect.
What fails in a perimembranous VSD?
Fusion of endocardial cushion tissue and the conal ridges with the muscular septum, which should close the interventricular foramen by about week 7.
Is a VSD cyanotic at birth?
No: the shunt is left to right; cyanosis appears only if pulmonary hypertension reverses the flow (Eisenmenger).
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Ventricular septation and the endocardial cushions
- Outflow tract: the spiral aorticopulmonary septum and neural crest
- Tetralogy of Fallot
- Atrioventricular septal defect (endocardial cushion defect)
- Atrial septal defect and patent foramen ovale
- Alcohol: fetal alcohol spectrum disorder
Related conditions
- Ventricular septal defect
- Heart failure
- Pulmonary hypertension and cor pulmonale
- Down syndrome (trisomy 21)
Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.
Sources: Langman's Medical Embryology, 13th ed., ch. 13: Cardiovascular System (Wolters Kluwer, 2015); Ventricular Septal Defect | Congenital Heart Defects (CHDs) | CDC (Centers for Disease Control and Prevention, 2024).
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Representative model, for educational purposes only.