The human arteries contain a thin delicate inner lining called endothelium. A healthy endothelium is necessary to get good erections. Endothelium uses nitric oxide to send signals to surrounding muscles. Upon receiving the signals from endothelium the muscles surrounding the arteries relax and blood rushes into arteries. The same process happens in arteries of penis to cause hard erections. Hence healthy arteries are required for healthy erections. When the cholesterol level increases in bloo...