We performed a multicenter, double-blind, randomized study to evaluate the effect of diltiazem on reinfarction after a non-Q-wave myocardial infarction. Nine centers enrolled 576 patients: 287 received diltiazem (90 mg every six hours) and 289 received placebo. Treatment was initiated 24 to 72 hours after the onset of infarction and continued for up to 14 days. The primary end point, reinfarction, was defined as an abnormal reelevation of MB creatine kinase in plasma within 14 days. Reinfarction occurred in 27 patients in the placebo group (9.3 percent) and in 15 in the diltiazem group (5.2 percent) — a 51.2 percent reduction in cumulative life-table incidence (P = 0.0297; 90 percent confidence interval, 7 to 67 percent). Diltiazem reduced the frequency of refractory postinfarction angina (a secondary end point) by 49.7 percent (P = 0.0345; 90 percent confidence interval, 6 to 73 percent). Mortality was similar in the two groups (3.1 and 3.8 percent, respectively, in the placebo and diltiazem groups), but adverse drug reactions (most of which were mild) were more common in the diltiazem group. Nevertheless, the drug was well tolerated, despite concurrent treatment with beta-blockers in 61 percent of the patients. We conclude that diltiazem was effective in preventing early reinfarction and severe angina after non-Q-wave infarction and that it was also safe and generally well tolerated. (N Engl J Med 1986; 315:423–9.), NON-Q-WAVE infarction, which was formerly referred to as nontransmural or subendocardial infarction, is usually associated with less myocardial necrosis and a lower in-hospital mortality than Q-wave or transmural infarction.1 2 3 4 5 6 Despite the initially favorable prognosis, however, long-term survival of patients after non-Q-wave infarction is similar to or even shorter than that after Q-wave infarction.1,4 5 6 7 8 9 It is now well documented that patients with non-Q-wave infarction are more prone to reinfarction, which occurs in the same area as the original injury.4 5 6 7 8 9 10 11 Thus, it appears that after a non-Q-wave infarction, viable but jeopardized myocardium remains within the perfusion zone of the infarct-related vessel, rendering.