Sildenafil (Generic Viagra®) is in a class of medications called phosphodiesterase (PDE) inhibitors. This treats erectile dysfunction by increasing blood flow to the penis during sexual stimulation. This increased blood flow can cause an erection and also treats PAH by relaxing the blood vessels in the lungs to allow blood to flow easily. The Food and Drug Administration announced the approval of Viagra (sildenafil citrate), the first oral pill to treat impotence, a dysfunction that affects millions of men in the United States March 1998.