Left main coronary artery (LMCA) atresia is a rare congenital heart disease and can be fatal in pediatric patients. We report an adult case of LMCA atresia, in which heart failure developed without episodes suggesting angina. A 40-year-old man presented with difficulty breathing. Echocardiography revealed diffuse hypokinesis of the left ventricle with an ejection fraction of 22% in the absence of significant valvular disease. A diagnosis of heart failure was made, and diuretics, enalapril, bisoprolol and warfarin were administered. Coronary angiography demonstrated no trace of the ostium of the LMCA in the sinuses of Valsalva; the middle to distal part of the LMCA was visualized by rich collateral flow from the right coronary artery to the left anterior descending coronary artery and left circumflex coronary artery. No trace of the ostium of the LMCA from the aorta or main pulmonary artery was detected on computed tomography angiography or echocardiography. The patient underwent coronary artery bypass grafting and a final diagnosis of congenital atresia of LMCA was made. The clinical course was uneventful and computed tomography angiography, performed 5 days after surgery, showed a patent bypass graft. This case demonstrates the importance of considering LMCA atresia even in the absence of chest symptoms suggesting angina in patients with heart failure.