Carcinoid syndrome produces valvular disease primarily involving-

The carcinoid syndrome : results from bioactive compounds such as serotonin released by carcinoid tumors . systemic manifestations include flushing, diarrhea, dermatitis, and bronchoconstriction. Carcinoid hea disease refers to the cardiac manifestation caused by the bioactive compounds and occurs in half of the patients in whom the systemic syndrome develops. The serotonin secreted by carcinoid tumors can produce fibrous plaques in the endocardium and right-sided cardiac valves, occasionally affecting left-sided valves, as well. Valvular lesions may be stenotic or regurgitant. ref : Robbins Basic pathology,9th edition,pg no.395 ref : harrisons book of internal medicine 20th ed