The extent of the opening may vary from pin size to complete absence of the ventricular septum, creating one common ventricle.

The ventricular septum consists of an inferior muscular and superior membranous portion and is extensively innervated with conducting cardiomyocytes.

The membranous portion, which is close to the atrioventricular node, is most commonly affected in adults and older children in the United States.

[citation needed] VSD is an acyanotic congenital heart defect, aka a left-to-right shunt, so there are no signs of cyanosis in the early stage.

[6] Congenital heart disease, particularly VSDs, is the number one cause of death for children with Down syndrome ages birth to two.

In the fifth week of gestation, the heart undergoes multiple processes of septation and forming a dextral loop.

Interfering with the latter leads to insufficient leftward movement of the ventricular outflow tract over the atrioventricular canal, which in turn can result in a VSD or, in the most extreme cases, a double outlet right ventricle with one.

[9][10] A ventricular septal defect arises when the superior part of the interventricular septum, which separates the right and left ventricles of the heart, fails to fully develop.

[12] This effect is more noticeable in patients with larger defects, who may present with breathlessness, poor feeding and failure to thrive in infancy.

Smaller congenital VSDs often close on their own, as the heart grows, and in such cases may be treated conservatively.

[16] The Amplatzer septal occluder was shown to have full closure of the ventricular defect within the 24 hours of placement.

[17] There have been some reports that the Amplatzer septal occluder may cause life-threatening erosion of the tissue inside the heart.

Critical attention is necessary to avoid injury to the conduction system located on the left ventricular side of the interventricular septum near the papillary muscle of the conus.

Once the repair is complete, the heart is extensively deaired by venting blood through the aortic cardioplegia site, and by infusing Carbon Dioxide into the operative field to displace air.

Multiple muscular VSDs are a challenge to close, achieving a complete closure can be aided by the use of fluorescein dye.