A 45-year-old man has daily temperatures up to 100.9°F and a 15 lb weight loss over 3 months. He has pallor, normal vitals, and normal cardiovascular and pulmonary exams except a low-pitched diastolic rumble at the apex that disappears when he lies on his right side. Hemoglobin is 10 g/dL. Most likely diagnosis?
A) Iron deficiency anemia
B) Infective endocarditis
C) Hyperthyroidism
D) Thalassemia