Incidence of cardiac malformations at birth and later, and neonatal mortality.

Malformations of the heart are found in about 8 of every 0OOO births. In addition, about 4 of every 0OOO births have bicuspid aortic valves, but they are rarely recognized early in life. Apart from these, ventricular septal defect is much the commonest malformation, forming about 30 per cent of all others. Probably small ventricular septal defects and bicuspid aortic valves are common because they have few drawbacks during the reproductive period so are hardly checked by natural selection. Atrial septal defect and persistent ductus arteriosus come next, each forming about IO per cent. Pulmonary stenosis and aortic coarctation each form about 7 per cent. Aortic stenosis and Fallot's tetralogy form about 6 per cent and transposition of the great trunks 4 per cent. These 8 malformations are responsible for 8o per cent of the total, but many less common ones have been listed.