Background: Type 2 diabetes is one of the most common chronic disorders worldwide and is an important cause of cardiovascular disease. Studies investigating the risk of atrial and ventricular arrhythmias in diabetic patients taking different oral diabetes medications are sparse. Methods: We used IBM MarketScan Medicare Supplemental Database to examine the risk of arrhythmias for patients on different oral diabetes medications by propensity score matching. Results: We found that patients on metformin monotherapy had significantly reduced risk of atrial arrhythmias, including atrial fibrillation, compared with monotherapy with DPP4 (dipeptidyl peptidase 4 inhibitor) or thiazolidinedione medications. Patients on metformin monotherapy had significantly reduced risk of atrial arrhythmias, ventricular arrhythmias, and bradycardia compared with monotherapy with sulfonylureas. Combination therapy with sulfonylureas and metformin had an increased risk of atrial arrhythmias compared with some other combinations. Conclusions: Different oral diabetes medications have significantly different long-term risk of arrhythmia. Specifically, metformin is associated with reduced risk of atrial fibrillation and ventricular arrhythmias compared with sulfonylureas.