This study sought to identify whether left atrial strain can predict new-onset atrial fibrillation (NOAF) in patients with heart failure (HF) and sinus rhythm.Both HF and atrial fibrillation have common risk factors, and HF is a risk factor for the development of atrial fibrillation and vice versa.Among 4,312 consecutive patients with acute HF from 3 tertiary hospitals, 2,461 patients with sinus rhythm and peak atrial longitudinal strain (PALS) were included in the study. Reduced PALS was defined as PALS ≤18%, and the primary endpoint was 5-year NOAF.During a 5-year follow-up, 397 (16.1%) patients developed NOAF. Patients with reduced PALS had higher NOAF than their counterparts (18.2% vs. 12.7%; p < 0.001). After adjustment for significant covariates, we identified 6 independent predictors of NOAF, including age >70 years (hazard ratio [HR]: 1.50; 95% confidence interval [CI]: 1.12 to 2.00), hypertension (HR: 1.45; 95% CI: 1.10 to 1.91), left atrial volume index ≥40 ml/m (HR: 2.03; 95% CI: 1.48 to 2.77), PALS <18% (HR: 1.60; 95% CI: 1.18 to 2.17), HF with preserved ejection fraction (HR: 1.47; 95% CI: 1.11 to 1.95), and no beta-blocker prescription at discharge (HR: 1.48; 95% CI: 1.14 to 1.92). A weighted score based on these variables was used to create a composite score, HAS-BAP (H = hypertension; A = age; S = PALS; B = no beta-blocker prescription at discharge; A = atrial volume index; P = HF with preserved ejection fraction [range 0 to 6] with a median of 3 [interquartile range: 2 to 4]). The probability of NOAF increased with HAS-BAP score.2In patients with HF and sinus rhythm, 16.1% developed NOAF, and PALS could be used to predict the risk for NOAF. The HAS-BAP score allows determination of the risk of NOAF. (Strain for Risk Assessment and Therapeutic Strategies in Patients With Acute Heart Failure [STRATS-AHF] Registry; NCT03513653).