As soon as Zenegra Tablets is ingested, the main ingredient Sildenafil Citrate starts its work by inhibiting the PDE5 enzyme. Inhibition of this natural enzyme causes a boost in the levels of nitric oxide and cGMP enzyme. These compounds are responsible for dilation of arteries and relaxation of the penile muscles. This way blood flow increases to the male reproductive region and leads to rigid and hard erection which last longer. Therefore, after consuming Zenegra it is possible to achieve stiff, long-lasting erection. The effect of this drug stays for four to five hours, giving you enough time to engage in sexual activities. One must remember that Sildenafil present in Zenegra at recommended doses has no effect in the absence of sexual stimulation.