Six cases of acute myocardial infarction with blood in the pericardial sac are described. In one case rapid death followed myocardial rupture leaving no time for the possibility of intervention. Of two other cases acute symptoms developing after myocardial rupture, one was operated on promptly and the other, whose condition improved on pericardiocentesis, after a delay of a few hours. Both are now long term survivors A fourth patient probably had two episodes of rupture which apparently sealed off. He underwent cardiac catheterization, but no epicardial leak was found. Subsequently at operation a sealed myocardial rupture was detected and sutured over. The fifth patient suffered a silent myocardial rupture. A false aneurysm was diagnosed four months later and he withstood successful surgery. In the sixth patient, the course was similar to that of case 1, namely rapid death with a clinical picture suggestive of tamponade. Postmortem examination showed a covert rupture with some evidence of attempts to plug the opening. The purpose of this report is to emphasize the varying course which myocardial rupture can take.