Heart failure (HF) is a complex condition resulting from structural or functional heart diseases that impair the ability of the heart to fill with or pump out blood. The main manifestations of HF are shortness of breath and tiredness which may limit the ability to exercise or perform simple daily physical activities such as walking. Heart disease leading to HF is associated with reduced muscle mass and reduced strength and low blood levels of testosterone; a hormone normally produced by the human (male and female) body. Recent studies have shown improvements of symptoms and ability to exercise in patients with heart failure receiving testosterone.