Sildenafil is the primary active ingredient of kamagra 100mg. PDE5 inhibitors include Sildenafil . This enzyme opens blocked arteries and enlarges blood vessels. In addition to relaxing the muscles, tissues, and pelvic region, it raises the body's levels of cGMP and nitric oxide. The blood arteries pump more blood into the penis because they may easily expand and contract for extended periods of time.The penis can fill with enough blood to pressurize and maintain it when the pelvic muscles relax.