A 60-year-old woman presented with ST-elevation myocardial infarction due to extrinsic compression of the left main coronary artery (LMCA) caused by a dilated pulmonary artery (PA) with idiopathic pulmonary hypertension and was successfully treated with intravascular ultrasound- and optical coherence tomography-guided stenting. Continuous subcutaneous epoprostenol infusion therapy was initiated immediately after the procedure and increased aggressively. Imaging modalities were extremely useful in making the diagnosis and providing follow-up of LMCA compression syndrome in this case. Over the one-year observation period, a sufficient hemodynamic improvement was obtained, without exacerbation of the PA dilatation, resulting in the absence of compression of the LMCA.