Background: It is well known that cigarette smoking is the risk factor of lung cancer, chronic obstructive pulmonary disease and ischemic heart disease. But there are few reports about the immediate effect of cigarette smoking on the cardiopulmonary functions. The serum level of carbon monoxide increases during cigarette smoking. It is known that carbon monoxide increases respration rate, heart rate and cardiac output, with decrease in maximal oxygen consumption. So we have studied to determine the immediate effects of cigarette smoking on the cardiopulmonary function during exercise. Method: Thirteen healthy smoking male subjects were included in this study. Each subject was undertaken pulmonary function test and incremental exercise test on two separate days, one without smoking (control) and the other after smoking three cigarettes per hour for five hours. The order of the two tests was randomized. Results: 1) The mean age of the subjects was $25{pm}4.9$ year-old and the mean smoking history was $6{pm}5$ pack years. 2) The mean blood level of carbon monoxide on the smoking day was higher than that on the nonsmoking day ($5.97{pm}1.34%$ vs. $1.45{pm}0.83%$; p<0.01). 3) The mean maximal oxygen consumption on the smoking day was lower than that on the nonsmoking day ($2.09{pm}0.32$ L/min vs. $2.39{pm}0.32$ L/min; p<0.05). 4) The mean anaerobic threshold on the smoking day was lower than that on the nonsmoking day ($1.33{pm}0.24$ L/min vs. $1.53{pm}0.20$ L/min; p<0.05). 5) The mean heart rate at rest on the smoking day was higher than that on nonsmoking day ($84.38{pm}11.06$ beats/min vs. $75.46{pm}5.83$ beats/min; p<0.05). But the means of maximal heart rate on both days were not different. 6) The pulmonary function tests were similar on both days. Conclusion: There was no change in pulmonary function test, but the maximal oxygen consumption and anaerobic threshold were decreased on the smoking day. So it was concluded that cigarette smoking impaired the cardiovascular functions immediately during exercise.