Individuals of O blood group have significantly lower plasma levels of either Factor VIII (FVIII) or the von Willebrand factor (vWF). Conversely, there is accumulating evidence that elevated FVIII-vWF levels may represent an important risk factor for ischemic heart and venous thromboembolic disease. In this study, individuals exercised for 20 minutes at 10% below the first ventilatory threshold (aerobic threshold), which corresponds to 48% of maximum oxygen uptake. People with non-O blood group show higher resting and postexercise vWF levels compared with those of O blood group, as evidenced by a lower maximal heart rate. The groups were compared using the ANOVA one-way test, and a P < 0.05 was considered statistically significant. These results could change the way in which exercise training is designed for both healthy and sick individuals because O group individuals could have a more thrombogenic response to exercise.