Heart failure (HF) is a growing health problem, at least in part due to the concurrent obesity epidemic plaguing developed countries. However, once a patient develops HF, an elevated BMI appears to confer a survival benefit--a phenomenon termed the "obesity paradox." The exact explanation for this paradox has been difficult to ascertain. Numerous plausible mechanisms have been asserted, including the fact that obese patients tend to be younger and more symptomatic, leading them to seek medical attention earlier in the course of their HF. Obese patients may also have larger energy reserves that help to offset the catabolic changes seen with HF. Other hypotheses highlight the limitations of BMI as an obesity classifier. The purpose of this review is to examine the various theories for the obesity paradox in HF and discuss the implications for the clinical management of obese patients with HF.