16 cases of left ventricular-right atrial communication are reported. The most consistent clinical features, suggestive of this condition, were: auscultatory findings of V.S.D., electrocardiographic patterns of right atrial enlargement and biventricular hypertrophy, considerable right atrial enlargement coexisting with signs of left-sided cardiac enlargement and increased polmonary vascularity to Xray examination, echocardiographic fluttering of the tricuspid valve. Cardiac catheterization revealed an increased oxygen content in the right atrial or ventricular blood without the passage of the catheter through an A.S.D. The definitive diagnosis was established by left ventricular angiocardiography which demonstrated immediate opacification of a dilated right atrium through a septal defect; the location of the septal defect in the cardiac septum was attempted. In patients who suffered from a large left to right shunt were recommended for surgical treatment also in view of the relatively bad tolerance of this defect and low operative risk. There were two deaths: one baby died of early congestive failure. 9 cases were operated upon with one immediate postoperative death. The remaining, controlled by clinic follow-up, had good results.