Obesity is becoming a global epidemic in both children and adults, and it is associated with numerous comorbidities such as coronary heart disease, stroke/cerebrovascular disease, type 2 diabetes, hypertension, certain cancers, and sleep-disordered breathing. Over the past 2 decades, the incidence of and mortality from coronary heart disease and cardiovascular diseases has been continuously declining. In contrast, the incidence of and mortality from heart failure (HF) have been increasing, with HF diagnosed in approximately 5 million Americans and 550,000 new cases diagnosed each year and a death rate looming at 300,000 per year. Over the years, conventional risk factors including hypertension, type 2 diabetes, and dyslipidemia have been implicated for these unsavory statistics, and recently many studies have highlighted the important role of obesity as an independent risk factor for HF. Here, the authors review the available literature on the effects of overweight and obesity on a variety of cardiac structural adaptations and alterations, the effects on left ventricular systolic and diastolic function, and their role in the development and prognosis of HF. Numerous studies have demonstrated an "obesity paradox" regarding prognosis, however, in that obese patients with established HF tend to have a more favorable prognosis than do lean patients. Finally, the authors discuss the role of cardiopulmonary exercise testing in the risk stratification of obese patients with advanced HF.