We recently encountered an interesting case of acute inferior ST segment elevation myocardial infarction (STEMI). This patient had a rare anatomic variation, single coronary artery. The right coronary artery originate from the left circumflex proper artery, not from aorta, was totally obstructed with thrombi. Though it took more time to figure out the patient's coronary anatomy and the culprit lesion, we successfully performed primary percutaneous coronary intervention within the guideline-recommended time period. We performed left coronary angiography at the beginning. This strategy could be helpful in determining the culprit lesion and preventing unnecessary procedural delay in acute inferior STEMI.