Background: The outcome of a coronary artery aneurysm at the bifurcation of the left coronary artery caused by Kawasaki disease affects myocardial involvement, which is related to the left ventricular function and outcome of patients. Methods: A total of eighteen (13 males, 5 females) patients with left main truncus occlusion between 1978 and 2022 were reviewed based on their medical records and selective coronary angiograms. Results: Most patients had a giant aneurysm at the bifurcation of the left coronary artery. There were two groups based on the timing of the left main trunk occlusion. In the one-time occlusion group, all seven patients had nearly fatal cardiac events. In the second-step occlusion group, 8 (73%) of 11 patients had asymptomatic occlusions of the left main trunk; they underwent grafting to the left anterior descending artery. The median ages at the left main trunk occlusion in the one-time and the second-step group were 18.1 years (range 4.9 to 26.3) and 25.0 years (2.2 to 45.0), respectively. In the second-step group, the median interval from the coronary artery bypass grafting to the left main truncus occlusion was 7.9 years (6 days to 24.5 years). Their left ventricular ejection fraction ranged from 20 to 65% (mean 49%). Conclusion: To prevent either a fatal cardiac event or a low left ventricular function, a coronary artery bypass graft to the left anterior descending artery was recommended at an optimal time in each patient with a giant aneurysm of the left main trunk complicating a stenotic lesion of the left anterior descending artery.