We report on 4 new cases of valvular heart disease in Parkinson's disease patients treated with the ergot derivative dopamine agonists pergolide and cabergoline. Noninflammatory fibrotic degeneration of cardiac valves has been reported to occur in patients with carcinoid syndrome and to occasionally complicate therapies with the anti-migraine ergot alkaloid ergotamine and methysergide and with the appetite suppressants fenfluramine and dexfenfluramine. In these cases, the pathogenesis is suspected to involve serotonin-mediated abnormal fibrogenesis by means of the 5-HT2B receptors, which are expressed in the fibroblasts of heart valves. Based on strikingly similar echocardiographic and histopathological features, we strongly suspect that ergot-derived dopamine agonists may cause a valvular heart disease nearly identical to that seen in those conditions. These cases add to a rapidly growing and worrying list of similar published reports, suggesting that we may well be facing a novel, yet unrecognized, complication of this class of agents, which are widely used not only in Parkinson's disease but also in restless legs syndrome and various common endocrine dysfunctions. Therefore, until more is known about the true prevalence of this side effect, we propose that an assessment of cardiac function be performed before and in the course of a long-term therapy with ergot derivative dopamine agonists.