Penile erections happens when after sufficient sexual stimulation, a man is sexually aroused and after which brain sends messages to the blood vessels in the penis. After a man is sexually aroused the blood vessels supplying blood to the penis widen and open up to allow more blood to flow inside at the same time, the veins get closed so that less amount of the blood can move out of the penis. Once blood enters the penis, the pressure of the blood traps the blood within the penile region resulting in a firm and hard erection.When the flow of blood stops and the veins open, the penis becomes slack. Sildenafil present in Silagra tablets constrains the actions of cGMP-specific phosphodiesterase type 5 (PDE5) which causes dilapidation of cGMP present inside the penis. The cGMP present inside the penis increases the flow of blood to the penis by dilating or widening penile blood vessels. The enzyme cGMP is also responsible for the relaxation of the smooth muscles in penis which leads to more blood inflow to the penis and restricted blood outflow from the penis resulting in stronger and firm erection. One must remember that sildenafil does not create an erection and only enhances the blood flow underneath the penis, hence, a thorough prior sexual stimulation is required in order to get the best results of this medication.