Viagra (sildenafil citrate) 30 tablets 50mg is a phosphodiesterase type 5 inhibitor, which works by enhancing the effects of nitric oxide in the penis and allowing blood to flow into the penis more easily. Viagra is a drug that treats erectile dysfunction in men. Erectile dysfunction is when a man cannot get or keep a stronger and longer erection. It can be caused by physical or emotional factors. Viagra increases blood flow to the penis, which helps a man achieve and maintain an erection when a man is sexually stimulated. It also provides stamina and better performance and increases the duration of sexual activity.