The present investigation was undertaken to evaluate the effects of Dilazep, a new antiplatelet and coronary dilating drug, on the exercise tolerance of patients who had suffered previous myocardial infarction and were participating in a cardiac rehabilitation programme. Seventy-two patients were enrolled in the study. They were randomly allocated to two groups of 36 subjects; patients in group A took Dilazep, 300 mg daily; patients in group B took acetylsalicylic acid, 100 mg daily, or dipyridamole, 300 mg daily. Before and after treatment all patients underwent two maximal or symptom limited cycloergometer stress tests, respectively 30 and 60 days after the episode of acute myocardial infarction. Total exercise time, maximum workload reached, heart rate, blood pressure, double product and oxygen pulse were measured. In both groups a significant increase in both total exercise time and maximum workload reached was recorded at the second stress test; this may reflect a greater degree of physical conditioning due to the rehabilitation programme. In group A patients total exercise time increased from 457.12 +/- 5.36 sec to 588.28 +/- 8.24 sec (p less than 0.005), in group B patients it increased from 459.18 +/- 6.11 sec to 547.43 +/- 7.47 sec (p less than 0.005). The mean values of maximum workload reached increased in group A from 4512.14 +/- 116.47 kgm to 5288.57 +/- 145.38 kgm (p less than 0.005), and in group B from 4522.22 +/- 108.42 kgm to 5098 +/- 137.51 kgm (p less than 0.005). Thus the exercise tolerance improved more in patients taking Dilazep than in those taking acetylsalicylic acid or dipyridamole.(ABSTRACT TRUNCATED AT 250 WORDS)