Genetically predicted atrial fibrillation presented no statistically significant association with overall breast cancer (odds ratio [OR] = 1.00; 95% confidence interval [CI]: 0.97–1.04; p = 0.79), estrogen receptor (ER) + (OR = 1.00; 95% CI: 0.96–1.03; p = 0.89) or ER− subtypes (OR = 1.00; 95% CI: 0.97–1.04; p = 0.89). This evidence concerns the gene ESR1 and atrial fibrillation.