Tadalafil, the active ingredient in Tadarise Pro 40 mg, works by inhibiting the enzyme phosphodiesterase type 5 (PDE5). This results in increased levels of cyclic guanosine monophosphate (cGMP) in the corpus cavernosum of the penis, which leads to relaxation of the blood vessels and increased blood flow. This process helps achieve and maintain an erection in response to sexual stimulation.