Using Holter monitoring the Authors compared the effectiveness of diltiazem 120 mg every 8 hours for three consecutive days with the results of a placebo administered with the same regimen, following a double-blind completely balanced cross-over trial in 20 patients with angina at rest. During treatment with diltiazem the total number of recorded ischemic episodes was 100, during treatment with placebo the total number was 357 (Tab. I); P less than 0.01 at analysis of variance (Tab. II). Ischemic episodes during treatment with diltiazem had a shorter duration (3.9 versus 5.1 min.), less marked ST segment shifts (1.3 versus 2 mm), and were less symptomatic (20% versus 29%) than ischemic episodes during placebo (Tab. III). No significant differences at a paired t test were noted. Diltiazem was more effective in the morning (12 p.m. - 12 a.m.: from 187 to 34 ischemic episodes) than in the evening (12 a.m. - 12 p.m.: from 170 to 66 ischemic episodes) (Fig. 1); P less than 0.01 at the chi-square test (Tab. IV). Diltiazem reduced the number of ischemic episodes with ST segment elevation, peaking of T waves and negative T wave inversion (from 188 to 39) more than the number of episodes with ST segment depression (from 169 to 61) (Tab. V); P less than 0.05 at the chi-square test. In conclusion, in patients with angina at rest, diltiazem reduces the incidence and seems to reduce the severity of ischemic episodes, too.(ABSTRACT TRUNCATED AT 250 WORDS)