Patients with essential thrombocythemia (ET) are at increased risk of developing arterial thrombosis. We report a case of a 36-year-man with unstable angina in the presence of occlusion of two coronary arteries with insufficient collateral perfusion. We also found essential thrombocythemia in this patient. The patient underwent coronary artery bypass grafting (CABG). Ten days before surgery, the aspirin was replaced by a prophylactic dose of low-molecular-weight heparin. Postoperative follow-up was complicated by pulmonary embolisms and a cardiac tamponade. We conclude that ET is a risk factor for coronary heart disease that should be treated with aspirin. If a patient needs CABG, aspirin should be continued because of the high risk of thromboembolic events in the high-risk ET patients. (Neth Heart J 2010;18:378-80.).