The authors investigated the effect of a single dose of 4 mg molsidomine on the course of bicycle ergometry. This effect was compared with that of 120 mg isosorbide dinitrate retard and with placebo. Isosorbide dinitrate in this large dose significantly protracted the period before angina pectoris developed after exercise, it significantly reduced the duration of stenocardias, significantly increased the total work output, significantly prolonged the period before a reduction of the ST segment occurred on the ECG and significantly reduced the values of reduction of the ST segments. Moisidomine in medium doses significantly protracted the period before angina pectoris developed after exercise and significantly increased the total work output. After comparison of the described results with those of investigations where smaller doses of isosorbide dinitrate were used, the authors assume that after increasing the dose of molsidomine its effect will be comparable with large nitrate doses.