Acute dyspnea is a major complaint of patients admitted to cardiology and emergency departments (ED). Acute dyspnea can be life-threatening, and is seen in cases of asthma, pulmonary embolism, acute heart failure and myocardial infarction. The present case is that of a 32-year-old man admitted to the ED with orthopnea position and agitation. Physical examination, electrocardiogram (ECG), transthoracic echocardiogram (TTE), contrast-enhanced computed tomography (CECT) of thorax and coronary angiography (CAG) helped to rule out chest disease pathologies such as pneuomo-thorax, pulmonary embolism and coronary artery disease, but were not enough to make an appropriate diagnosis in this case. Because of high pretest probability of aortic dissection, transesophageal echocardiography (TEE) was performed and a diagnosis of Stanford type A dissection closing left main coronary artery (LMCA) ostia from beat to beat was made.