Causes for a ventricular septal defect include:

• Congenital heart disease:
• Abnormal development of the heart in the womb
• Heart attack

The ventricular septum is the wall that separates the lower chambers of the heart, called the ventricles. A ventricular septal defect creates a disturbance in blood flow through the heart. Such a defect allows blood to flow from the left ventricle to the right ventricle. This can damage the right ventricle and damage the lungs.