Acute coronary syndrome is defined as a condition which is followed by new onset of chest pain due to acute ischemia that leads to myocardial injury. According to definition of acute coronary syndrome, based on electrocardiographic (ECG) presentation, it is divided into three groups: ST- segment elevation myocardial infarction (STEMI), non-ST- segment elevation myocardial infarction (NSTEMI) and unstable angina. The purpose of this review paper is to succinctly review recent progress in the knowledge of MINOCA - myocardial infarction with nonobstructive coronary arteries that presents without ST-segment elevation. MINOCA still remains a puzzling clinical entity and an enigma due to lack of understanding the precise pathogenesis of this condition. This review paper is composed of six chapters, each of them dealing with different aspects of approaching and understanding sudden onset chest pain in a patient without ST-segment elevation on ECG, increased troponin level in blood stream and with no finding of significant coronary artery stenosis (<50%) after coronarography is done. Part one describes the types of acute coronary syndrome, its epidemiology, clinical presentation and different electrocardiographic (ECG) presentation. A part two shift focus to epidemiology and prevalence of MINOCA and leads to conclusion that it differs widely from classic myocardial infarction like STEMI and also shows that these patients have fewer traditional cardiac risk factors. Parts two, three, four and five explain some of the most common causes and explain underlying pathophysiology entities that could lead to this uncommon clinical presentation in patients. Also, these parts explain which methods are recommended to diagnose such entity; which approach is shown to be the most successful according to the European Cardiology Society and other available meta-analysis. Finally, adequate diagnosis of underlying pathophysiology cause is crucial for planning the best targeted therapy in order to provide recovery and improve quality of life and prognosis in these patients.