The compression of the left main coronary artery (LMCA) secondary to pulmonary artery trunk dilatation is a relatively new entity that has been associated with severe pulmonary hypertension. It is associated with acyanogen congenital cardiopathies or idiopathic pulmonary arterial hypertension. The natural history is unknown and its treatment has been based more on the severity of the angiographic compression than on the objective demonstration of myocardial ischemia. We report a case of a woman with severe pulmonary arterial hypertension due to an atrial septal defect with extrinsic compression of the LMCA and a physiopathologic approach to guide its treatment.