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Previous studies have shown that exercise increases platelet reactivity in patients with coronary artery disease (CAD). However, the response of platelet reactivity to exercise is considerably variable and its predictors are poorly known.We studied 214 consecutive patients (age 61.9 ± 9 years, 167 men) with stable angina and obstructive coronary artery disease. All patients underwent a symptom-limited treadmill exercise stress test. Venous blood samples were collected before and at peak exercise. Platelet reactivity was assessed by the platelet function analyzer system as the time for flowing whole blood to occlude a collagen–adenosine diphosphate ring (closure time: shorter times = higher reactivity). Both closure time at peak exercise and the exercise-induced change in closure time from rest were assessed as an expression of exercise-related platelet reactivity.Closure time decreased significantly with exercise in the whole population (from 95.9 ± 22 to 81.2 ± 18 s, P < 0.001). The only variable significantly associated with closure time at peak exercise was hematocrit (P = 0.003). Basal systolic blood pressure (P = 0.023) and lack of nitrate use (P = 0.03), on the contrary, were the only variables significantly associated with increased exercise-induced closure time change. Peak hematocrit maintained an independent association with peak closure time in multivariable analysis, although the correlation was mild. No variable, on the contrary, was associated with exercise-induced platelet reactivity after correction for basal closure time values at multivariable analyses.Among stable coronary artery disease patients, platelet reactivity after exercise cannot be reliably predicted by several common clinical and laboratory variables.