Objective To investigate the feasibility and clinical value of medical history and clinical manifestation-based protocol(MHCMP) for the diagnosis of spontaneous coronary artery dissection(SCAD)using intravascular ultrasound (IVUS).Methods Based on the MHCMP designed in our centre,intraoperative sequential analysis was performed in patients with acute coronary syndrom and clinical tip of SCAD,SCAD and its classification were defined according to the result of IVUS.Results Of the 37 patients admitted with ACS at the Cardiology Service,29 patients had SCAD as the cause(78.4 ％).All the patients underwent coronary angiography and IVUS,of which 9 patiens were type I (24.3 ％),15 patients were type Ⅱ (40.5％) and 5 patients were type Ⅲ (13.5％).The left anterior descending artery was the most frequently affected (16 patients),followed by the the right coronary artery (7 patients),while 5 patients had dissection of the circumflex artery and 1 patient had dissection of the left main coronary artery.Type I (evident arterial wall stain):this was the pathognomonic angiographic appearance of SCAD with contrast dye staining of the arterial wall with multiple radiolucent lumens.Type Ⅱ (diffuse stenosis of varying severity):this angiographic appearance was not well appreciated and was often missed or misdiagnosed.SCAD commonly involved the mid to distal segments of coronary arteries,and could be so extensive that it reached the distal tip.There was an appreciable (often subtle) abrupt change in arterial caliber,with demarcation from normal diameter to diffuse narrowing.This diffuse and usually smooth narrowing could vary in severity from inconspicuous mild stenosis to complete occlusion.Type Ⅲ (mimic atherosclerosis):this appearance was the most challenging to differentiate from atherosclerosis and most likely to be misdiagnosed,while IVUS was helpful for the differential diagnosis.Conclusions MHCMP is able to screen out all kinds of SCAD and guide the treatment decisions making.