You are answering a USMLE-style medical question. Question: A 55-year-old man is brought to the emergency department 12 hours after the sudden onset of shortness of breath and substernal chest pain at rest; the pain is increased by inspiration. He has also had a nonproductive cough, fever, and malaise for the past 5 days. He does not smoke or use illicit drugs. His temperature is 38°C (100.4°F), pulse is 125/min, respirations are 32/min, and blood pressure is 85/45 mm Hg. Physical examination shows distended neck veins. Auscultation of the chest discloses bilateral basilar rales and muffled heart sounds. An ECG shows sinus tachycardia, diffuse ST segment elevation, low voltage QRS complexes, and fluctuating R wave amplitude. Which of the following is the most likely diagnosis? Options: A) Kawasaki disease B) Rheumatic fever C) Infective endocarditis D) Cardiac tamponade Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.