Essential thrombocythemia (ET) is an uncommon type of myeloproliferative disorder, characterized by both thrombotic and hemorrhagic diatheses. No clear guidelines exist for the pre- or post-operative management of patients with ET undergoing cardiac surgery. Here, we present a rare case of a patient with essential thrombocythemia and severe aortic stenosis, who needed an aortic valve replacement on cardiopulmonary bypass and who suffered no complications.