In the United States, obesity has reached epidemic proportions. Results from the 2003-2004 National Health and Nutrition Examination Survey estimated that 66% of US adults are either overweight (body mass index [BMI] 25-30 kg/m(2)) or obese (BMI>30 kg/m(2)) as defined by the BMI cutoffs established by the World Health Organization. In the 1970s, only 15% of the US population between the ages of 20 and 74 years was categorized as obese. In 2003, approximately 32% of the adult population was obese. Obesity plays an important role in the evolution of cardiovascular disease. This article reviews the histopathophysiologic changes that occur in cardiac structure and function in response to obesity, explores the relationship between obesity and arrhythmias such as atrial fibrillation and sudden cardiac death, and analyzes electrocardiographic changes in an obese patient.