Excess body weight increases the risk for many disorders including cardiovascular disease and such patients have a greater risk for developing heart failure (HF). Despite evidence demonstrating the adverse effects of excess weight, the relationship between body mass index (BMI) and mortality in HF patients remains controversial. Paradoxically, several large cohort studies have shown that overweight and obese HF patients seem to have better survival than their healthy weight counterparts. The exact mechanism for this "obesity paradox" is not fully understood. Proposed mechanisms include a greater tolerance to angiotensin-converting enzyme inhibition, higher serum lipid levels, and the alteration of inflammatory cytokine metabolism in obese patients. Although the relationship between elevated BMI and improved survival has been well documented, recent clinical trials have not addressed this association. In 65 of 75 clinical HF trials reviewed, BMI as a potential independent predictor of outcomes was not addressed. Furthermore, the variation of pharmacokinetics in the obese population has been dealt with to a limited degree. If data concerning BMI and weight loss is to directly impact treatment recommendations for HF patients, well-designed clinical trials are needed.