PDE5 inhibitors are NOT to be used with ‘nitrate' drugs, which treat certain forms of heart disease. PDE5 inhibitors help the body's natural response to sexual stimulation, since they block the enzyme Phosphodiesterase-5 in the smooth muscle cells in the penis. The oral medications for Erectile Dysfunction, impotence, are called, Phosphodiesterase-5, or PDE5 inhibitors in short.