A 15 month old black male who developed near fatal intravascular hemolysis two days after repair of an ostium primum septal defect with a teflon patch is presented. One month after initial operation, reoperation was required for control of hemolysis. At that time a piece of pericardium was placed over the underendothelialized left atrial side of the patch and the mitral cleft was repaired. He initially did well but within several days developed mitral regurgitation. Hemolysis recurred two months postoperatively, but then spontaneously subsided. We propose that the recurrent mitral insufficiency created a defect in the pericardial patch and that caused recurrent hemolysis. Normal endothelial ingrowth probably covered this small defect and hemolysis subsided. Following the second hemolytic episode six months ago, the patient continues to do well.