Long-term survival of patients with partial atrioventricular septal defect (PAVSD) without operative therapy is very rare. The case is reported of a 75-year-old man who presented with dyspnea and decline of general condition. A heart defect was known but not investigated as the patient refused to undergo invasive cardiologic diagnosis. Hence, treatment was conservative. At autopsy, a huge (3 cm diameter) ostium primum atrial septal defect (ASD) was found, together with deformation of the right and left atrioventricular valves and extreme dilatation of the heart. Pulmonary arteriosclerosis indicating pulmonary hypertension was present, but there was no lung fibrosis. Life expectancy in patients with PAVSD ranges from 3 to 37.5 years. The present patient showed very late onset pulmonary hypertension, which may be a critical parameter for survival.