This study sought to determine the impact of regular alcohol consumption on left atrial (LA) mechanical and reservoir function.Earlier studies suggest that regular alcohol intake is associated with increased atrial fibrillation (AF) and LA dilatation.This study prospectively enrolled 160 patients with paroxysmal or persistent AF to undergo 3-T cardiac magnetic resonance (CMR) imaging in sinus rhythm. Patients self-reported alcohol consumption in standard drinks (∼12 g alcohol) per week over the preceding 12 months and were categorized into 4 groups: 1) lifelong nondrinkers; 2) mild drinkers (3 to 10 standard drinks/week); 3) moderate drinkers (11 to 20 standard drinks/week); 4) heavy drinkers (>20 standard drinks/week). Permanent AF and cardiomyopathy were excluded. On CMR, maximum LA volume (LA) and minimum LA volume (LA), global LA emptying fraction (LAEF) as (LA - LA) / LA, and LA reservoir function as (LA - LA) / LA were calculated.maxRegular alcohol consumption (mean 15.8 ± 6.9 standard drinks/week, n = 120) was associated with larger LA size (LA volume index 50 ± 13 ml/m vs. 43 ± 12 ml/m; p = 0.005), reduction in LAEF (40 ± 14% vs. 52 ± 15%; p < 0.001), and reduction in reservoir function (77 ± 48% vs. 119 ± 63%; p < 0.001) compared with lifelong nondrinkers (n = 40). There were progressive dose-related impairments in LAEF (mild 45.4 ± 13.5% vs. moderate 39.1 ± 14.7% vs. heavy drinkers 35.6 ± 12.6%; p < 0.01) and reservoir function (mild 95.8 ± 55.6% vs. moderate 74.8 ± 47.1% vs. heavy drinkers 61.7 ± 34.4%; p < 0.01). Predictors of atrial mechanical dysfunction included weekly alcohol intake (p = 0.001), older age (p = 0.018), and persistent AF (p = 0.016), but not binge drinking or beverage type.2In patients with AF, habitual alcohol consumption is associated with significantly increased LA size and atrial mechanical dysfunction compared with nondrinkers.