Previous studies suggested that statin therapy reduces the risk of occurrence and recurrence of atrial fibrillation mainly in patients with coronary artery disease. Data regarding the effect of statins on the risk for the entire range of supraventricular arrhythmias (SVA) in mild heart failure (HF) with different disease causes are lacking. Multivariate Cox proportional hazards regression models were used to assess the effect of statin therapy, evaluated as a time-dependent covariate, on the risk of SVA and recurrent SVA (defined as atrial fibrillation, atrial flutter, atrial tachycardia, and supraventricular tachycardia) that were inappropriately treated with implantable cardioverter-defibrillator device in 1,790 patients enrolled in the Multicenter Automatic Defibrillator Implantation With Cardiac Resynchronization Therapy trial. Statin users constituted 68% of the study patients (n = 1209). They were older and more frequently men; they were more likely to have ischemic cardiomyopathy, diabetes, hypertension, and previous atrial arrhythmias. During the 3.7-year median follow-up time, 160 patients had an SVA event, and the total number of recurrent events was 335. Time-dependent statin therapy was independently associated with a significant 29% reduction of the first SVA event (p = 0.046) and 33% reduction of recurrent SVA events (p = 0.003), consistent across all prespecified subgroups. In conclusion, in mild HF with either cardiac resynchronization therapy with a defibrillator or an implantable cardioverter-defibrillator device, statin therapy was associated with significant reduction of occurrence and recurrence of inappropriately treated SVA.