A 73-year-old woman had an episode a week ago in which she became disoriented, had difficulty speaking, and had persisting weakness on the right side of her body. On physical examination, she is now afebrile with pulse of 68/min, respirations of 15/min, and blood pressure of 130/85 mm Hg. On auscultation, the lungs are clear, the heart rate is irregular, and there is a midsystolic click. A chest CT scan shows a focus of bright attenuation within the heart. An echocardiogram shows that one valvular leaflet appears to balloon upward. The ejection fraction is estimated to be 55%. Laboratory findings show serum creatine kinase (CK), 100 U/L; glucose, 77 mg/dL; creatinine, 0.8 mg/dL; calcium, 8.1 mg/dL; and phosphorus, 3.5 mg/dL. Which of the following is the most likely diagnosis? Carcinoid heart disease