<prompt> Answer this question truthfullyWhat is the reason for left-sided valvular lesions not being seen in a patient with carcinoid heart disease?  <response>: <reason> Left-sided valvular lesions are not seen in a patient with carcinoid heart disease because the blood passes through the lung, which contains monoamine oxidase MAO, converting 5-hydroxytryptamine 5-HT to 5-hydroxyindoleacetic acid 5-HIAA before reaching the left heart. 