A 54-year-old man presented to the emergency department with sudden onset of palpitations. His medical history included stage IV renal cell carcinoma, end-stage COPD, NYHA class IV heart failure, recent pulmonary embolism, and ongoing tobacco abuse. Cardiac examination revealed atrial flutter and a rapid ventricular rate. The patient was given a diltiazem infusion, which restored normal sinus rhythm within 24 hours.