For many men, trouble getting or keeping an erection, formally known as erectile dysfunction, is often an early warning sign of heart disease or other circulatory problems. Atherosclerosis, the same disease process that clogs coronary arteries with cholesterol-filled plaque, does the same thing to the arteries that supply blood to the penis. Since an erection depends on extra blood flow to the penis, any obstructions can prevent an erection from occurring. According to Erectile Dysfunction, a Special Health Report from Harvard Medical School, blood vessel problems are the leading cause of erectile dysfunction and serve as an early warning sign of trouble in the heart or elsewhere in the circulatory system. Simple lifestyle changes like losing weight, exercising more, or stopping smoking can improve erections, as can Viagra and other erectile dysfunction drugs, devices, and sex therapy.