Background: Cholesterol lowering therapy may offset the development of coronary atherosclerosis, and the resulting reduction in coronary ischemia may be observed in the electrocardiogram(ECG). Methods: A total of 2039 Japanese adults with hypercholesterolemia were divided into two groups(receiving 10-20 mg pravastatin daily or a normal diet) and were followed up for 5 years. ECG studies were performed at entry and every year during the follow-up period. The occurrence of myocardial infarction and the appearance or worsening of ischemic ST changes were assessed in terms of effects on the ECG. Results: Of the 2039 patients registered, 827 were excluded from the study for various reasons. Consequently, a total of 1212 patients were analyzed. There was a lower degree of worsening in the pravastatin group(n=757) than in the normal diet group(n=455) in the primary prevention cohort[11(1.8%) vs. 16(4.3%), respectively, P=0.031]. On the other hand, there was no difference in the frequency of worsening between the two groups in the secondary prevention cohort[7(4.4%) in the pravastatin group vs. 4(4.9%) in the diet group, P=0.25]. Event-free survival was better in the pravastatin group than in the normal diet group in the primary prevention cohort(P=0.011), but there was no difference between the two groups in the secondary prevention cohort. Conclusions: These results suggest that pravastatin may reduce the incidence of coronary heart disease and that this effect may be predominantly observed in patients with early atheromatous lesions. Background: Cholesterol lowering therapy may offset the development of coronary atherosclerosis, and the resulting reduction in coronary ischemia may be observed in the electrocardiogram (ECG). Methods: A total of 2039 Japanese adults with hypercholesterolemia were divided into two groups (receiving 10-20 mg pravastatin daily or a normal diet) and were followed up for 5 years. The occurrence of myocardial infarction and the appearance or worsening of ischemic ST changes were assessed in terms Of was 2039 patients registered, 827 were excluded from the study for various reasons. There was a total of 1212 patients were analyzed. There was a lower degree of worsening in the pravastatin group (n = 757) than in the normal diet group (n = 455) in the primary prevention cohort [11 (1.8%) vs. 16 (4.3%), respectively, P = 0.031]. On the other hand, there was no difference in the frequency of w orsening between the two groups in the secondary prevention cohort [7 (4.4%) in the pravastatin group vs. 4 (4.9%) in the diet group, P = 0.25]. Event-free survival was better in the pravastatin group than in the normal diet group in the primary prevention cohort (P = 0.011), but there was no difference between the two groups in the secondary prevention cohort. Conclusions: These results suggest that pravastatin may reduce the incidence of coronary heart disease and that this effect may be predominantly observed in patients with early atheromatous lesions.