A 53 year old man complained of chest pain during an exercise treadmill test. Electrocardiogram revealed transient giant R-wave, right-axis deviation, intraventricular conduction delay, and ST-segment elevation in the inferolateral leads. Subsequent coronary angiography showed an 80% lesion in mid part of a nondominant left circumflex artery, whereas the other coronary arteries had mild atherosclerosis only. Percutaneous coronary intervention and stenting was performed on the left circumflex artery lesion. A follow-up exercise thallium scan 3 months later still showed an intermediate-sized, mild reversible perfusion defect in the inferior and lateral wall but the giant R-wave ECG pattern was not inducible anymore. Restudy coronary angiography showed no in-stent restenosis, but there was disease progression in the midpart of the right coronary artery. The initial electrocardiographic pattern is typical of the "giant R-wave syndrome." Severe coronary spasm superimposed on the underlying mild atherosclerotic lesion of the right coronary artery is hypothesized to be the cause of the initial event. Ad hoc direct stenting was performed on the right coronary artery lesion. The patient remained symptom-free with a normal thallium scan 9 months later.