Tadaflo is used to treat male erectile dysfunction (impotence) and pulmonary arterial hypertension (PAH). Part of the physiological process of erection involves the release of nitric oxide (NO) in the corpus cavernosum. This then activates the enzyme guanylate cyclase, which increases cyclic guanosine monophosphate (cGMP) levels, leading to smooth muscle relaxation in the corpus cavernosum, resulting in an increased inflow of blood and an erection. When sexual stimulation causes the local release of nitric oxide in the corpus cavernosum, then nitric oxide activates the enzyme guanylyl cyclase, which results in increased levels of cGMP. The increased levels of cGMP in the corpus cavernosum produce smooth muscle relaxation and inflow of blood into the penile tissues, thereby producing an erection. PDE5 degrades cGMP in the corpus cavernosum, and the inhibition of PDE5 by Tadaflo maintains increased levels of cGMP in the corpus cavernosum. Tadaflo does not affect penile blood flow in the absence of sexual stimulation.