Tadalis tablets 20mg (generic Cialis) contain tadalafil, which acts on the erectile tissue of the penis to increase blood flow to cause an erection. During sexual stimulation nitric oxide is released in the erectile tissue of the penis which activates the enzyme guanylate cyclase. This enzyme increases levels of a chemical called cyclic guanosine monophosphate (cGMP), which relaxes the blood vessels in the penis and allows blood to fill the spongy erectile tissues to cause an erection. Another enzyme called phosphodiesterase type 5 (PDE5) breaks down cGMP preventing blood flow into the penis, which causes loss of an erection. Tadalis tablets 20mg inhibit the action of PDE5 which resolves erectile dysfunction by allowing the natural process of sexual stimulation to activate the cGMP mechanism for achieving and maintaining an erection.