Principal Findings:

A total of 8037 patients were randomized to atenolol, and 7990 to control.

Vascular mortality during the treatment period (days 0-7) was significantly lower (2p less than 0.04) in the treated group, (3.9% versus 4.6%), but this 15% relative difference had wide 95% confidence limits (from 1 to 27%). No subgroups were identified in which the relative reduction in days 0-7 was clearly better, or clearly worse, than 15%.

At one year, overall vascular mortality was significantly lower for the atenolol group (life-table estimates: 10.7% atenolol vs 12.0% control; 2p less than 0.01).

A substudy reviewed records for 193 of 217 early deaths (79 allocated to atenolol and 114 allocated to control). There was a lower rate of deaths attributed to myocardial rupture or electromechanical dissociation in the atenolol group. There was a slightly higher incidence of fatal ventricular fibrillation and aortic dissection in the control group, and of bradycardia/asystole in the atenolol group. The data did not indicate any substantial contribution from mechanisms such as limitation of infarct size or prevention of reinfarction or cardiac arrest.