A 51-year-old man was seen in the emergency department with a complaint of malaise, diarrhea, and weakness 1 week after starting treatment with hydrochlorothiazide, 25 mg per day, to treat hypertension. He had no other known medical history, was a lifetime nonsmoker, and had no family history of coronary artery disease. His blood pressure was 110/75 mm Hg, and his pulse rate was 100 beats per minute and regular. Results from a 12-lead electrocardiogram (ECG) were obtained (Figure 1).