The purpose of this study was to examine the relationship between smoking and cardiopulmonary function, and the effect of smoking habit on exercise tolerance after discharge from the hospital, focusing on CPX test data of patients hospitalized for acute myocardial infarction, and on CPX test data at 6 months after discharge. A total of 123 male patients hospitalized for acute myocardial infarction between April 2014 and December 2020 were included. Laboratory and CPX data were compared between smokers and non-smokers. CPX data of smokers, ex-smokers and non-smokers were also compared in 24 patients who underwent CPX examination 6 months after discharge. HDL-C was significantly decreased (p < 0.05) and τON was significantly prolonged (p < 0.05) during hospitalization in smokers. τON was significantly shorter only in ex-smokers (p < 0.05) 6 months after discharge compared to during hospitalization. These results suggest that τON, which reflects the oxygen uptake kinetics of peripheral tissues, is shortened by smoking cessation.