In vivo upregulation of miR-1 through atrial injection of a recombinant lentivirus carrying miR-1, resulted in enhanced downregulation of KCNE1 and KCNB2 and, unlike what may be expected, caused an increase in delayed rectifier potassium current (IKs) and AF susceptibility. The gene discussed is KCNE1; the disease is atrial fibrillation.