A patient in their 50s presented to the emergency department with dyspnea, palpitations, fatigue, and syncope for 4 days. Ten days prior, the patient developed a fever after experiencing symptoms of an upper respiratory tract infection. They had no history of cardiovascular disease. On presentation, the patient’s blood pressure was 98/65 mm Hg, heart rate was 65 beats per minute, and body temperature was 36.6 °C. In addition, their serum troponin I level was 12.8 ng/mL (normal range, <0.10 ng/mL; to convert to µg/L, multiply by 1.0) and N-terminal pro–B-type natriuretic peptide was 13 800 pg/mL (normal range, <300 pg/mL; to convert to ng/L, multiply by 1.0). Transthoracic echocardiography showed a left ventricular ejection fraction of 34% with hypokinesia of the interventricular septum and left anterior and right ventricular walls. Coronary angiography showed no stenosis. The patient’s blood pressure dropped to 60/40 mm Hg after admission to the hospital. The initial electrocardiogram (ECG) (Figure, A) showed a wide QRS complex tachycardia. One day later, the patient developed complete atrioventricular block, for which they required temporary pacing. When the patient returned to the ward, an ECG was obtained (Figure, B).