57 patients were admitted to the study, 3-6 weeks after acute myocardial infarction. They received either placebo or 1 mg/kg tiapamil intravenously according to a randomized, double-blind procedure. The study had two objectives: (a) to assess the effect of tiapamil on work tolerance and exercise-induced myocardial ischemia; (b) to demonstrate possible antiarrhythmic effects against exercise-induced arrhythmias. The duration of exercise and physical work capacity increased slightly in both groups, these effects, however, not reaching statistical significance. On the other hand, the number of exercise-induced extrasystoles did not change significantly under placebo but decreased from 30.9 to 14.8 beats/min after tiapamil (p < 0.01). No side effects were observed. While the hemodynamic effects of tiapamil in patients with coronary artery disease are yet to be elucidated, our findings confirm the efficacy of this calcium antagonist against exercise-induced ventricular premature beats in patients with coronary artery disease.