Surgical treatment of acute aortic dissection in a patient with idiopathic dilated cardiomyopathy is rare. A 57-year-old man diagnosed with idiopathic dilated cardiomyopathy with left ventricular dimension of 59 mm in diastole, left ventricular dimension of 47 mm in systole, and fractional shortening of 0.19 on echocardiography developed type A acute aortic dissection. Emergency surgery was conducted for ascending aorta and hemiarch repair for ascending aorta redissection and dilation. The postoperative course was uneventful under appropriate hemodynamic control. Standardized criteria for aortic dissection in a patient with poor left ventricular contraction have not established, but surgery should be considered for all patients in good preoperative condition when it is the only effective life-saving alternative.