Left posterolateral short atrioventricular Mahaim pathway connecting the left atrium to the left ventricular epicardium

Key Teaching Points•Left-sided Mahaim pathways are rare, and their electrophysiological and anatomical characteristics have not been well studied.•Electrophysiological study revealed that the mechanism of the tachycardia was antidromic atrioventricular reciprocating tachycardia using a left-sided Mahaim pathway.•Detailed mapping, including that inside the coronary sinus, revealed that the Mahaim pathway was considered as a short atrioventricular pathway connecting the left atrium to the left ventricular epicardium. •Left-sided Mahaim pathways are rare, and their electrophysiological and anatomical characteristics have not been well studied.•Electrophysiological study revealed that the mechanism of the tachycardia was antidromic atrioventricular reciprocating tachycardia using a left-sided Mahaim pathway.•Detailed mapping, including that inside the coronary sinus, revealed that the Mahaim pathway was considered as a short atrioventricular pathway connecting the left atrium to the left ventricular epicardium.