A ventricular septal defect (VSD) is a type of heart defect (congenital heart disease) in which there is a hole in the wall (septum) between the heart's lower chambers (ventricles). It is the most common congenital heart defect.

VSDs vary in size, from a mere pinpoint to the almost total absence of septum. Also, they may occur in isolation or as part of a more complex series of congenital defects. The symptoms and severity of a VSD depend on how large it is. The vast majority are small, without symptoms and spontaneously close within the first three years of life.

Larger VSDs, however, can be dangerous. Because the pressure in the left side of the heart is greater than the pressure in the right side, the hole allows blood to seep from the left ventricle into the right ventricle. This results in too much blood volume in the right side of the heart and lungs. The more blood that is diverted to the right side of the heart, the harder the lungs and right ventricle must work. Eventually, the stress on the right ventricle can cause it to weaken and/or enlarge (dilate) to compensate for the increased workload, resulting in symptoms associated with heart failure.

Also, the lungs can become congested upon receiving more blood than is needed, which can result in either infection of the lungs and/or pulmonary hypertension (high blood pressure in the lung’s blood vessels). Additionally, VSD may raise the risk of the formation of blood clots (which could lead to stroke), and the development of abnormal heart rhythms (arrhythmias).

For VSDs that remain open, most physicians agree that no matter how small the hole is, it should be treated sooner rather than later – especially if other defects are present. However, in some cases, the VSD may actually encourage the mixing of blood from the left and right sides of the heart, which can be beneficial in the setting of complex heart defects that do not allow blood to travel through the heart in a normal fashion. In this case, the VSD may actually be beneficial, and surgeons will wait to treat the VSD until the more serious congenital defects can be corrected. Treatment usually involves surgery.