The engorgement of the penis with blood leads to penile erection. When blood delivers by the blood vessels to penis the engorgement appears. Under normal conditions, sexual stimulation provokes the production and release of nitric oxide in the penis,which activates the enzyme, guanylate cyclase, which results the production of cyclic guanosine monophosphate (cGMP). This enzyme affects the quantity of blood that the blood vessels deliver and remove from the penis. That is necessary for the erection. Viagra Super Active (Sildenafil) also decreases the tension in the pulmonary artery in a serious condition called pulmonary arterial hypertension. By blocking an enzyme called phosphodiesterase-5 (PDE5) which destroys the cGMP sildenafil doesn’t allow the destruction of cGMP and allows cGMP to accumulate and persist longer.