Background: Cardiac rehabilitation reduces mortality and morbidity rate of patients with coronary artery diseases (CAD); however, acute exercise stimulation may also increase the thrombotic risk through platelet activation. Studies on the effects of cardiac rehabilitation on platelet function have been sparse. Methods: A total of 28 patients (24 men and 4 women; average age = 54.6 +/- 8 years old) with stable CAD were enrolled in this study and divided into Aspirin-treated (n =11; Aspirin group) and dual-antiplatelet-treated group (DAPT group; n =17). Symptom-limited cardiopulmonary exercise test (CPET) with a cycle ergometer was performed on all the patients. Before and after CPET, platelet function was evaluated using light transmission aggregometry and whole blood flow cytometry. Results: All patients completed the CPET without provoked cardiac events, and the mean value of peak oxygen uptake (Peak Vo(2)) was 19.3 +/- 3 ml/(kg min). Prior to CPET, platelet aggregation was significantly suppressed in DAPT group compared to Aspirin group (43.0 +/- 21.5 vs. 72.9 +/- 7.5,p < 0.001). CPET promoted platelet aggregation in Aspirin group (72.9 +/- 7.5 vs. 80.9 +/- 7.6, p= 0.005) and DAPT group (43.0 +/- 21.5 vs. 50.1 +/- 20.9, p= 0.010), and platelet count was increased in Aspirin (210.9 +/- 54.6 vs. 227.5 +/- 58.1, p= 0.001) and DAPT group (217.5 +/- 63.8 vs. 229.7 +/- 63.7, p= 0.001). However, the expression levels of CD62p and PAC-1 were not affected by CPET in both groups. Conclusion: Symptom-limited CPET enhanced platelet aggregation in patients with CAD despite treatment with antiplatelet, mainly via platelet count augmentation, but not through single platelet activation.