Mahaim fibre coexisting with anomalous origin of the left main coronary artery from the right aortic sinus and an interarterial course.

We present the case of a 45-year-old female with a normal heart, who exhibited an episode of a broad QRS tachycardia that was initially suggested to be sustained ventricular tachycardia. Coronary angiography showed the left main stem originating from the right aortic sinus with an interarterial course between aorta and right ventricular outflow tract. Electrophysiological study revealed the presence of a right atriofascicular accessory pathway with decremental antegrade conduction (Mahaim bundle), which was successfully ablated.