Ninety one patients with unstable angina were evaluated by clinical and angiographic study. Of 91 patients, 42 (46%) responded poorly to the intensive medical treatment. Emergency coronary arteriography was then performed on these patients. The important pathoanatomical mechanisms contributing to instability of angina pectoris and/or refractoriness to the intensive medical treatment were observed in 19 of 42 patients (45%). These include: 1) More severe disease with left main lesion; 2) Refractory coronary spasm; 3) Coronary dissection; 4) Rapid progression of atherosclerosis; 5) Ulcerating plaque and 6) Coronary thrombus. Our results presented here suggest that an appropriate knowledge regarding pathophysiology might improve the approach to treatment.