In a randomized controlled trial 31 patients, who were unsuccessfully being treated with metoprolol for severe angina pectoris, were also given molsidomine or placebo. During an exercise test, there was no difference between the groups in heart rate or blood pressure. There was a tendency towards a mild, significant improvement in exercise performance in the molsidomine-treated group, in whom both workload and exercise duration increased after two weeks of treatment. In the placebo-treated group, these parameters decreased.