The mechanism of myocardial infarction in patients with nonobstructive coronary artery disease remains unknown. The SOFT-MI study has been designed as a single-center, prospective observational trial to investigate the prevalence of vulnerable and disrupted plaques in patients with acute MI but without any significant coronary stenosis (defined as stenosis of >50%) at coronary angiography. All patients will undergo coronary OCT immediately after coronary angiography. In addition, CMR will be performed within 1 week of coronary angiography to evaluate associated myocardial abnormalities as well as extracardiac findings. The study will provide insight into the mechanism of MI without obstructive coronary artery disease at coronary angiography, and may be useful in order to establish an appropriate therapeutic strategy for the secondary prevention of ischemic events.