In the past, patients with acute myocardial infarction were treated by putting them to bed. It was felt that once the symptoms and electrocardiographic signs of acute myocardial infarction had occurred, the process was complete and that the heart and patient at rest would allow the illness to run its course and the heart to heal. The focus of treatment in the Coronary Intensive Care Unit was to prevent complications of acute myocardial infarction, primarily arrhythmias leading to cardiac arrest and the treatment of cardiac arrest itself. Acute phase morbidity and mortality related to loss of myocardium through infarction has not changed. Post-discharge mortality and morbidity is, in large part, related to the occurrence of congestive heart failure, secondary to loss of myocardium to infarction. Efforts to preserve myocardium through pharmacologic intervention to limit demand, have not resulted in significant benefit. It is now recognized that the infarction is not complete on presentation, that it occurs as a wavefront over a period of four to six hours, and that in 80 to 90 percent of patients, infarction is due to thrombus in the infarct-related artery. Therefore, reperfusion of the jeopardized myocardium during this window of four to six hours could result in salvage of myocardium with resultant decrease in acute mortality as well as acute and chronic morbidity and mortality from myocardial failure.