Background: The purpose of our study was to examine whether left ventricular dyssynchrony predicts left main coronary artery stenosis in patients with non-ST-segment elevation myocardial infarction. Methods: A total of 100 consecutive patients with non-ST-segment elevation myocardial infarction underwent echocardiography and coronary artery angiography. The 3-dimensional echocardiography-derived left ventricular dyssynchrony parameter was determined by using the standard deviation of the time to the minimal systolic volume for the 16 segments. A stenosis  50% of the diameter of the left main coronary artery or a stenosis  70% in 1 or more of the major epicardial vessels or their main branches was considered significant. Results: The logistic regression analysis revealed that this parameter (odds ratio 1.2; 95% confidence interval, 1.01-1.42; p = 0.04) was the independent predictor of left main coronary artery stenosis. The receiver operating characteristic curve analysis revealed 8.86 as the optimal cutoff value to predict left main coronary artery stenosis (sensitivity, 71.4%; specificity, 89.2%). Conclusions: The assessment of left ventricular dyssynchrony by 3-dimensional echocardiography is useful for a noninvasive diagnosis of the left main coronary artery stenosis in patients with non-ST-segment elevationmyocardial infarction.