“…6 Carcinoid heart disease is seen in approximately 50% of those who suffer from carcinoid syndrome, 7-10 which in turn occurs in 20% to 30% of patients with carcinoid tumor. 5 Long-lasting exposure to high levels of serotonin, which produces proliferative endocardial lesions, [8][9][10][11]12 causes carcinoid heart disease 3,8,9,11 ; i.e., formation of fi brotic plaques 7,10,13 on the heart valves results in shortening and thickening of the heart valves and fi nally incompetence of the valves. 3,5,7,8,10,11,13,14 Because morphological change of the heart valves caused by the endothelial plaques is irreversible even by lowering serotonin levels by somatostatin therapy and hepatic dearterialization, 10,11 valve surgery is the main treatment for carcinoid heart disease.…”