Like Cialis, Tadalis comprises of the active element Tadalafil which is the third member of the drug class phosphodiesterase type 5 (PDE-5) inhibitors. It is chemically and pharmacologically different from the previous 2 members Sildenafil citrate and Vardenafil. Tadalafil though, has similar mechanism of action like Sildenafil citrate and Vardenafil. It blocks the action of the enzyme PDE-5 which regulates the penile erections. Increased quantity of PDE-5 is known to cause restricted flow of blood in the penis which in turn leads to ED. Blockade of PDE-5 leads to increase in the levels of the biochemical nitric oxide and guanylyl cyclase which is an enzyme. Both this biochemical in synchronization, causes elevated synthesis of cGMP in the body near the penile region. The enzyme cGMP is known to cause vasodilation and is a potent vasodilator in the body. Hence, increased production of cGMP causes widening of blood vessels especially, the arteries that carry the blood to the penis from the heart. Also, under the influence of cGMP the smooth muscle below penis relax and allow the retention of more blood inside the penile arteries. This enhancement of blood flow to the penile region causes full-fledged penile erection which is sustained for a long time for satisfactory sexual intercourse.