The cause of heart failure is a weakened or thickened cardiac muscle. For example, in chronic high blood pressure (hypertension), the heart must pump extra forcefully against the additional blood pressure. First it becomes enlarged and thickened. But over time, the heart weakens, scarring (fibrosis) develops, and it becomes less efficient at pumping. It can become larger (dilated) and weak or thickened and stiff. When the risk factors for heart failure are present, there usually is inflammatory stress, which further damages the cardiac muscle depleting cells of energy and antioxidants.