The purpose of this study was to determine the effect of smoking marihuana and of high-nicotine cigarettes on exercise-induced angina pectoris. Smoking 1 marihuana cigarette increased the resting product of systolic blood pressure times heart rate 54%, increased the venous carboxyhemoglobin level, and decreased the exercise time until angina 50% in 10 patients with angina pectoris. Smoking 1 high-nicotine cigarette increased the resting product of systolic blood pressure times heart rate 36%, increased the venous carboxyhemoglobin level, and decreased the exercise time until angina 23%. Smoking either marihuana or high-nicotine cigarettes decreases exercise performance until angina by increasing myocardial oxygen demand and by decreasing myocardial oxygen delivery. Smoking 1 marihuana cigarette decreased the exercise time until angina more than smoking 1 high-nicotine cigarette (p less than 0.001).