Sildenafil Citrate and Vardenafil are same when it comes to the action mechanism. When these drugs enter the bodily system, the enzyme phosphodiesterase type five (PDE5) dramatically reduces. Reduction in PDE5 levels increases the levels of cyclic Guanosine Monophosphate and Nitric Oxide. These naturally activated compounds relax the penile muscles and dilate the arteries so that the blood flow to the penile shaft is increased. This way abundant amount of blood accumulates in a man's penile shaft to encourage the process of erection. Moreover, he can handle the erection for longer duration and delay his ejaculation. The effect of Silvitra in the body persists up to four to six hours. This means a man can achieve erection during every sexual stimulation and sustain it for longer period.