Apcalis Oral Jelly contains tadalafil as its active ingredient. Tadalafil inhibits the enzyme phosphodiesterase type 5 (PDE5), which is responsible for the degradation of cyclic guanosine monophosphate (cGMP) in the smooth muscle cells of the penis. By inhibiting PDE5, tadalafil helps to increase the levels of cGMP, leading to relaxation of the smooth muscles and increased blood flow to the penis, which results in an erection.