A 46-year-old white woman presented to the emergency department with hemodynamically stable sustained ventricular tachycardia (VT). She was chemically cardioverted with lidocaine. Her electrocardiogram, showing sinus rhythm, was unremarkable, and serial cardiac enzyme tests excluded myocardial infarction. A signal-averaged electrocardiogram was abnormal, with a filtered QRS duration of 187 milliseconds. Echocardiography showed normal left and right ventricular systolic function but revealed diastolic dysfunction of the left ventricle. Electrophysiologic testing revealed easily inducible sustained VT of 4 distinct morphologies. A diagnosis of possible arrhythmogenic right ventricular dysplasia was made based on the signal-averaged electrocardiographic and electrophysiologic findings. Cardiac magnetic resonance imaging showed no evidence of arrhythmogenic right ventricular dysplasia, however. An endomyocardial biopsy revealed noncaseating granulomas consistent with sarcoidosis. This case illustrates the importance of complete testing, including invasive studies such as endomyocardial biopsy, in patients presenting with life-threatening ventricular arrhythmias to establish a correct diagnosis.