Objectives: We sought to evaluate that dyssynchronous left atrial (LA) lengthening and contraction might predict future development of new onset atrial fibrillation (AF) in congestive heart failure (CHF). Background: The clinical and echocardiographic parameters to the risk of developing new onset AF in CHF have not been studied comprehensively. Methods: A total 158 patients who admitted for CHF without past or current AF were evaluated. We measured the time to peak velocity, peak strain, and strain rate with reference to QRS complex during ventricular systole (reservoir) and late diastole (atrial contraction) in mid portion of 4 LA walls. Dyssynchronous atrial lengthening and contraction (atrial dyssynchrony) was defined as the standard deviation of each parameter. Results: New onset AF developed in 21 patients (13.3%) after mean follow up of 43 짹 15 months. In univariate Cox analysis, older age, larger LA dimension and volume index, lower LA fractional shortening, and the presence of atrial dyssynchrony during reservoir period were associated with new onset AF, but not atrial dyssynchrony during atrial contraction period. In multivariate Cox analysis, atrial dyssynchrony based on strain during reservoir period (> 39msec, HR 10.0, p = 0.003) and LA size (> 45 mm, HR 4.3, p = 0.016) were independent predictors of new onset AF in CHF. Conclusions: We demonstrated that atrial dyssynchrony based on strain during reservoir period is the strongest univariate and multivariate predictor for new onset AF in hospitalized heart failure.