A cardiac electrophysiologic study (EPS) is a safe procedure with a low complication rate. We report here a case of severe stenosis of the left main coronary artery (LMCA) that was incidentally detected during an EPS; this was successfully managed by stenting the LMCA. The patient was a 75-year-old man with recurrent chest fluttering and no previous angina underwent EPS and he developed acute ischemic chest pain due to induced atrial fibrillation. The coronary angiography showed a critical stenosis in the distal LMCA. The patient underwent percutaneous coronary intervention with a sirolimus-eluting stent in the LMCA. The patient has remained asymptomatic during a 1-year follow-up period. To prevent potentially catastrophic complications, performing a stress myocardial imaging test should be strongly considered before conducting EPS in elderly patients.