In TIMI II, patient entry began in April 1986 and ended in June 1988 with enrollment of 3,534 patients. Patients were treated with intravenous rt-PA within four hours of the onset of chest pain thought to be caused by myocardial infarction and randomly assigned to an invasive strategy or a conservative strategy. The primary endpoint was survival free of recurrent myocardial infarction at six weeks and one year of follow-up. There were 1,681 patients assigned to the delayed invasive strategy in which catheterization was performed between 18 and 48 hours after rt-PA therapy. If catheterization showed a greater than 60 percent subtotal stenosis of the infarct-related artery that was considered to be technically approachable, angioplasty was attempted. Angioplasty was performed in 60.5 percent of the 1,500 patients who underwent catheterization in the invasive strategy group. The remaining 39.5 percent or 593 patients did not have angioplasty performed. There were 1,658 patients assigned to a conservative strategy in which cardiac catheterization was reserved for the 587 patients who had spontaneous or exercise-induced myocardial ischemia within 21 days of infarction. A total of 13.5 percent of patients in this arm underwent coronary angioplasty, 7.6 percent underwent bypass surgery, and 1.1 percent underwent both procedures; 77 percent of the patients in the conservative strategy group had no revascularization procedure within 21 days of infarction.