Introduction: This study aimed to evaluate the extent of baseline cardiac remodeling present in patients with new-onset cardiomyopathy (CM) with and without atrial fibrillation (AF). AF concurrent with heart failure is associated with increased morbidity and mortality. There is limited research comparing the extent of cardiac remodeling present in patients with new-onset CM associated with AF (AF-CM group) to that present in patients with new-onset CM without any concomitant or antecedent dysrhythmia (CM group). Methods and Results: Patients with a left ventricular ejection fraction ≤40% without a prior history of CM were identified from our healthcare system’s electronic medical records for the period of January 1, 2012 to September 30, 2016. Those with an antecedent or concomitant diagnosis of AF comprised the AF-CM group, and those with no prior dysrhythmia comprised the CM group. The AF-CM group (n=196) was compared with the CM group (n=197). The groups were controlled for left ventricular ejection fraction. Patients in the AF-CM group had more left atrial, right atrial, and right ventricular remodeling, more advanced right ventricular systolic dysfunction, and increased severity of both tricuspid and mitral regurgitation at presentation than the CM group. Conclusion: Patients with new-onset CM with AF had greater global cardiac remodeling at presentation than those with CM not associated with AF.