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ABSTRACT Background and Aim: Cardiovascular diseases (CVD) are among the most important causes of death and disability all around the world. Blood cells, especially platelets, may play a crucial role in pathophysiology of these disorders. Considering the increased risk of thrombosis after acute physical activities, and the role of the platelets in these disorders, many nutritional approaches had been evaluated for the prevention of thrombosis. Recently, the effects of cocoa consumption on hemostasis have recently attracted the attention of many researchers. In this study we evaluated the effects of cocoa consumption on platelet count, mean platelet volume (MPV), and platelet distribution width (PDW), during one session of incremental exhausting aerobic exercise in male soccer players. Materials and Methods: This semi-experimental study included 20 healthy volunteer male soccer players (age: 22±1years BF%: 22.5±1.2 VO2max:52.6±1.5 ml.kg-1.min). After written consent, all subjects performed Bruce Test within two successive weeks. After the first blood sampling (stage one), 0.5 mg/kg of placebo (0.5 g cocoa powder in 300 ml of 4% sucrose solution) or cocoa solution (18.75 g cocoa powder in 300 ml 4% sucrose solution) was randomly given to the subjects. All cases performed Bruce Test two hours later. Blood samples were collected just before Bruce Test (second stage), immediately after Bruce Test ( third stage) and 1 hour after Bruce Test (fourth stage). After preparation of peripheral blood smears, platelet count, MPV and PDW were measured by Mindray cell counter. Using spss 16, data were analyzed by means of two-factor analysis of variance (ANOVA) and Bonfferoni test at the level 0.01. Results:Our results indicated a significant decrease in platelet count, MPV, and PDW after cocoa consumption (P<0.01). In addition, there was a significant difference between the 2 groups in these values after Bruse Test (P<0.01). However, in spite of significant increase in platelet count, MPV, and PDW after Bruse Test, cocoa consumption 2 hours before the test decreased these values significantly (P<0.01). Conclusion: Cocoa consumption before exhaustive physical exercises may prevent exercise induced increase in the platelet indices hence, potentially can prevent cardiovascular and thrombotic events and sudden death in the athletes. Key words: Cardiovascular disease, Platelet, Cocoa, Exhaustive exercise, Bruce Test Received: Jul 25, 2012 Accepted: Sep 10, 2012 Conflict of interest: None declared