The presence of a defect (opening) in the interventricular septum. While they are usually congenital, ventricular septal defects (VSDs) may also occur as a complication of myocardial infarction. Congenital VSDs are often associated with other congenital heart defects such as atrial septal defects, patent ductus arteriosus, and right aortic arch. While they may be asymptomatic if the defect is small, shunting of blood from the left ventricle to the right ventricle can cause right heart failure, resulting in progressive shortness of breath, hypoxemia, and cyanosis, if the defect is sufficiently large.