Introduction: Larger left atrial appendage (LAA) ostium area and greater left atrial (LA) volume have been associated with an increased risk of ischemic stroke. Catheter ablation (CA) of atrial fibrillation (AF) leads to morphological and functional changes within the LA and LAA, some of which are not well studied. Here, we present findings regarding post-ablation changes of the LAA ostia and correlate them with various LA, LAA and left ventricular (LV) functional and morphological metrics. Methods: This retrospective analysis included patients scheduled to undergo first-time radiofrequency CA for AF. Catheter ablation techniques included PVI with or without additional ablations. Cardiac magnetic resonance imaging (CMR) was used to assess LA, LAA and LV morphology and function, including LAA ostium area, LA/LAA volume and volume index, LA ejection fraction, LA strain, and LV ejection fraction. A Kruskal-Wallis test was used for correlating LAA ostial dimensions with other LA morphological and functional metrics. The t-test or two-sample Wilcoxon test were used to compare LA and LAA morphological parameters. Results: A total of 101 patients with AF were included in this study. The mean age was 60.1 ± 11.1 years, 69% were male, the average BMI was 29.22 ± 5.08. The LAA ostial area reduced significantly from 3.84 ± 1.15 cm 2 before ablation to 3.42 ± 0.96 cm 2 after ablation (p=0.0004). This reduction was asymmetrical, as the minor axis length decreased from 1.92 cm to 1.77 cm without significant changes in the major axis. LVEF increased from a pre-ablation average of 48.26% to a post-ablation average of 53.62% (p=0.015). Correlation of pre-ablation LVEF and LAA ostium area showed a near-significant negative trend (r=-0.21, p=0.083). LAEF correlated negatively with LAA ostial area (r=-0.289, p=0.0057), total LA strain (r=-0.248, p=0.0185), and passive LA strain (r=-0.208, p=0.049). Conclusion: There is a significant asymmetrical reduction of the LAA ostial area after AF ablation that is independent of LVEF changes. Larger LAA ostial area was associated with lower LAEF and LA strain. Remodeling of the LAA after AF ablation may help account for reduced risk of stroke and increased cardiac function.