Background: Left atrial volume can be accurately measured by real-time 3-dimensional echocardiography (RT3DE) without any geometric assumption. However, clinical impact of left atrial volume determined by RT3DE in patients with left ventricular dysfunction has not been demonstrated. Methods: In 73 patients with severe left ventricular dysfunction (ejection fraction: 27짹7%) and sinus rhythm, left ventricular end-systolic and end-diastolic volumes, and left atrial end-systolic (LAVs) and end-diastolic volumes (LAVd) were measured using RT3DE. At the same day, M-mode and 2D Doppler echocardiography were performed. Clinical observation was conducted during 5.1짹6.0 months. Results: During the follow-up period, 12 patients admitted to hospital due to heart failure and no patient presented cardiac death. Those 12 patients (16%) showed larger initial LAVs (124짹42 vs. 81짹30 ml, p<0.001) and LAVd (96짹41 vs. 58짹28 ml, p<0.01), higher transmitral E wave velocity, lower late diastolic mitral annular velocity, more severe mitral and tricuspid regurgitation, and higher maximal velocity of tricuspid regurgitation than those without clinical events. There was no significant difference between the two groups in initial left atrial diameter on M-mode echocardiography, E/E��� ratio, left ventricular volumes and ejection fraction, and the proportion of ischemic cardiomyopathy. Among all variables, LAVs showed the largest area under the curve (0.80, 95% confidence interval: 0.66-0.94) in ROC curve analysis for predicting cardiac events. LAVs ��� 93 ml predicted the events with sensitivity 83% and specificity 67%. Conclusion: LAVs determined by RT3DE is a strong predictor for heart failure in patients with severe left ventricular systolic dysfunction and sinus rhythm.