Kamagra contains Sildenafil citrate as the active ingredient. Before understanding the working mechanism of sildenafil citrate in Kamagra, one needs to first understand the scientific basis of a penile erection. After sufficient sexual stimulation, when a man is aroused, messages are sent to the brain to activate blood vessels in the penis. After the sexual arousal, the blood vessels carrying blood to the penis widen and open up to allow more blood to flow inside. Simultaneously, the veins are constricted so that the outflow of the blood from the penis is prevented. This leads to a firm and hard erection.Sildenafil present in this medication inhibits the cGMP-specific phosphodiesterase type 5 (PDE5) which causes degradation of cGMP. The cGMP present in the penile region increases the flow of blood to the penis by widening the blood vessels and relaxing the smooth muscles in penis. This results in stronger and firm erection which is sustained for long period of time to enable men to indulge in a satisfactory sexual activity. One should remember that this medication does not product erection on its own. It only widens the blood vessels and enhances the flow of blood into the penile region. Thus, a thorough sexual stimulation is essential in order to get the best result out of this medication.