Around twenty per cent of patients have cardiac valve abnormalities, usually affecting the right side of the heart. These lesions result from the formation of plaques on the valves, consisting of smooth muscle in a collagenous stroma. The most common findings are tricuspid incompetence and pulmonary stenosis, and these are often associated with severe right heart failure. Left-sided valve lesions in association with bronchial carcinoids are rarely found. Pellagra may occur, nicotinamide deficiency resulting from the increased conversion of 5-hydroxytryptophan into 5HT.
