A 58 year old man was admitted with a complaint of chest pain upon exertion during the previous 10 days, which was increasing in duration and intensity. The patient was hospitalised with a diagnosis of unstable angina. At electrocardiography, ST-T changes were observed in DII, DIII, and aVF. The patient’s blood pressure was 130/85 mm Hg, pulse rate 76 beats/min, and systemic findings were normal. Anti-ischaemic treatment, which included aspirin, β blocker, clopidogrel, heparin, statin, and angiotensin converting enzyme inhibitor, was initiated. During follow up, there was no increase in cardiac enzymes. The echocardiographic examination was normal. Following stabilisation with medical treatment, coronary angiography was performed. The left anterior descending artery and circumflex artery were completely normal. In the right coronary artery (RCA), consecutive non-significant lesions in the mid segment and severe stenosis on the posterior descending artery bifurcation in the RCA at the left anterior oblique position were determined. Slow contrast progression was observed in the region of the conus artery at the same position (panel A). In the right anterior oblique position, contrast caused by saccular dilatations originating from conus artery was detected (panel B), which decreased immediately (panel C) and virtually disappeared 10 minutes (panel D) after the catheter was withdrawn. A stent was implanted to resolve the severe stenotic lesion, and the patient was discharged after arrangements were made for medical treatment.