Four cases of aorto-pulmonary window are presented, diagnosed in the Section of Pediatric Cardiology during the last six years. The results obtained from clinic; ECG; X-ray; hemodinamic and angiographic studies are described. All of them were clinically diagnosed as left to right shunt through a persistent ductus arteriosus in two cases and of VSD the other two. The final diagnosis was made through cardiac cateterization in one case and at surgery in three. Two of the cases showed additional alterations, in one case it was a PDA, and the other a valvular aortic stenosis. All of them were operated, three successfully and one died immediately after operation. We consider that the study of this relatively rare cardiopaty deserves special attention, because of the similarity to other forms of left to right shunts. We insist on its difficult clinical dianose and the need of making a early diagnosis to do corrective surgery.