Recent case reports found an association between CYP2D6 activity and atrial fibrillation or abnormal heart electrophysiology (D’Urso et al., 2018; Mazer-Amirshahi et al., 2019), suggesting that CYP2D6 genetic variants affecting this enzyme activity should be considered in future studies. The gene discussed is CYP2D6; the disease is atrial fibrillation.