There is increasing evidence linking depression and cardiovascular disease. However, the authors could find no literature directly linking depression with atrial fibrillation or atrial flutter. The authors report the case of a patient with uncontrolled atrial arrhythmia who cardioverted to normal sinus rhythm after treatment of major depressive disorder (MDD) and posttraumatic stress disorder (PTSD) with venlafaxine. The authors discuss comorbidity of MDD and atrial fibrillation, and explore evidence of venlafaxine as an antiarrhythmic agent. Further research is needed to establish the clinical role of venlafaxine as a Class 1 antiarrhythmic agent and any association between atrial arrhythmias and MDD and PTSD.