Obesity is a known risk factor for developing cardiovascular disease, including heart failure. However, the impact of obesity on patients with heart failure is unclear. Weight reduction is a recommended method of prevention of cardiovascular disease. However, the phenomenon of the “obesity paradox” (or “reverse epidemiology”) revealed that overweight and mild to moderate obesity are associated with better outcomes in patients with heart failure compared with patients at normal or ideal weight. Even more, increases of weight in cachectic heart failure patients might improve survival, although patients with heart failure who are overweight or mildly to moderately obese have better outcomes than patients with heart failure who are at ideal or normal weight. In heart failure patients, weight reduction through diet regulation, moderate exercise, and bariatric surgery can improve quality of life and New York Heart Association functional class, but it is yet unclear if these measures will improve survival.