In order to establish the effects of 5-isosorbide mononitrate on: the exercise capacity, the onset period of angina and ischemia along with the degree and on whether the duration time was prolonged up to 5 hours after the oral administration of 20 mg of this drug, we compare this drug against a placebo in a group of 15 patients with stable angina pectoris developed by effort who performed an exercise test using a bicycle ergometer. After the administration of 20 mg of 5-isosorbide mononitrate it was observed that onset time of angina (p less than 0.001), the onset time of ST decrease (p less than 0.002) and total time of exercise attained were significantly superior to those found in patients with placebo administration. Moreover, for the same degree of EKG ischemia (ST decrease) showed a superior exercise time was registered (p less than 0.002) after the administration of 5-isosorbide mononitrate (5-IM). Our results show that an oral dosage of 20 mg of 5-IM given to patients with stable angina pectoris increased the capacity and exercise tolerance delaying significantly the onset time of angina, the onset time of EKG ischemia and its decree induced by the effort up to 5 hours after its administration.