The differentiation between ventricular tachycardia and broad-complex supraventricular tachycardia can be extremely difficult, particularly in emergency situations. We report a case of hemodynamically compromising broad-complex tachycardia in a 63-year-old man. The patient had previously sustained an anteroseptal myocardial infarction and had subsequently undergone coronary artery bypass surgery because of triple-vessel coronary artery disease. Intravenous treatment with ajmalin terminated the tachycardia and revealed preexcited QRS complexes compatible with the presence of a left-sided atrioventricular accessory pathway. An antidromic atrioventricular reentrant tachycardia (identical to the clinical tachycardia) was induced during an electrophysiologic study. In conclusion, there are several causes of broad-complex tachycardia, even in patients with previous myocardial infarction, and, where doubt exists, electrophysiologic studies should be performed.