Introduction: Atrial fibrillation is associated with increased risk of heart failure and mortality. The association of QRS duration (QRSd) with morbidity and mortality is understudied in patient with atrial fibrillation (AF) Hypothesis: We sought to investigate the association of prolonged QRSd (≥120 ms) and risk of heart failure and in-hospital death in patients admitted for AF with rapid ventricular response (RVR) Methods: A retrospective study in a community hospital using EPIC database analyzed 1637 patients from 2013-2018 with admission codes of AF with RVR. The cohort was then stratified based on QRSd ≥120ms vs <120ms. A p-value of <0.05 was considered significant Results: Among the 1637 patients who were admitted with AF with RVR, 233 (14%) had QRS ≥120ms. Patient’s characteristics with QRSd≥120 compared to those with QRSd<120ms were mean age [75.9 (11.8) vs 70.9 (13.6), (P<.0001)], history of CAD [41% vs 28%, odds ratio (OR)= 1.78, 95% confidence interval (CI): 1.3-2.3 (P<.0001)], history of PVD [15% vs 7%, OR=2.38, 95% CI: 1.58-3.59 (P<.0001)], history of acute MI [50% vs 33%, OR=1.99, 95% CI:1.5-2.6 (P<.0001)] and CHA2DS2Vasc score [median (IQR) 5(3, 6) vs 4(3, 5) (P<0.001). QRSd≥120ms was associated with higher BNP value [median (IQR) 537(305, 862) vs 371(186, 655) (P<0.001)] and an increased risk of heart failure [(70% vs 55%, OR=1.93, 95% CI:1.43-2.6 (P<.0001)]. Additionally, higher in-hospital mortality rate was observed in patients with QRSd≥120ms [4.3% vs 1.3%, OR=3.11, 95% CI:1.44-6.75 (P=0.006)] Conclusions: In patients who were admitted with AF with RVR, QRSd≥120ms was associated with a higher burden of cardiovascular disease, CHA2DS2Vasc score and an increased risk of heart failure resulting in worse clinical outcomes. Higher median BNP values suggest that worsening heart failure contributed to higher in-hospital mortality. Heart failure associated mortality could be alleviated with medical management or cardiac resynchronization therapy.