In this study we investigated the acute effects of cigarette smoking on cardiac function during exercise in 12 normal young males. Radionuclide angiocardiography was used to assess cardiac performance at rest and during upright-bicycle exercise on two consecutive days. On the second day each subject smoked three cigarettes. Exercise studies were continued until 85% of age-predicted heart rate for an individual was achieved. At rest cigarette smoking induced significant increases in resting heart rate, blood pressure, and contractility and significant decreases in end-systolic volume and pulmonary transit time. Comparison of hemodynamic data during exercise before and after smoking showed the only significant change to be a decrease in pulmonary transit time. These results suggest that cigarette smoking in healthy young males does not significantly alter cardiac function during submaximal exercise.