An orally available phosphodiesterase type 5 (PDE5) inhibitor with vasodilatory activity. Avanafil selectively inhibits PDE5, thus inhibiting the degradation of cyclic guanosine monophosphate (cGMP) found in the smooth muscle of the corpus cavernosa of the penis. The inhibition of cGMP degradation results in prolonged muscle relaxation, vasodilation, and blood engorgement of the corpus cavernosa, thereby prolonging penile erection.