Hole in the septum between the heart’s ventricles. Ventricular septum defect is a congenital heart disorder; only in exceptional cases does it occur spontaneously, for example after a heart attack in which part of the septum dies. The consequence of a congenital ventricular septum defect is that blood flows from the left ventricle (where blood pressure is high) to the right ventricle (where the pressure is much lower). This causes pressure to rise in the right ventricle, and thus also in the blood vessels of the lungs. The seriousness of the symptoms depends on the size of the defect: a small hole causes little or no discomfort but a large one may be accompanied by retarded growth, shortness of breath, rapid tiring and pneumonia. In a number of cases, minor defects heal of their own accord after a few years, so that treatment is not necessary. A heart operation to close the opening is carried out if the defect does not appear to be healing spontaneously or if the hole is large. In the latter case, it is preferable to carry out the operation within a few months of birth.