Secundum atrial septal defect associated with a cleft mitral valve.

Five cases of atrial septal defect are reported, each of which was associated with a cleft in the anterior or posterior (or both) leaflet of the mitral valve. Only 3 had a characteristic murmur of mitral regurgitation, and 2 of these patients were thought to have a partial endocardial cushion defect. In two patients, the discovery of the mitral valve cleft came only at the time of operation, when a thrill was noted over the posterior left atrium. A high index of suspicion is necessary at the time of operation, because preoperative diagnosis may be extremely difficult. Closure of the atrial septal defect alone may materially worsen the effect of the mitral regurgitation. It is emphasized that the diagnosis of this type of mitral valve pathology in patients with an atrial septal defect is an indication for bacterial endocarditis prophylaxis.