Yes my friend; good question too.

Viagra aka Sildenafil (Revatio) is used to improve the ability to exercise in people with pulmonary arterial hypertension (PAH; high blood pressure in the vessels carrying blood to the lungs, causing shortness of breath, dizziness, and tiredness).

Sildenafil is in a class of medications called phosphodiesterase (PDE) inhibitors.

Sildenafil treats PAH by relaxing the blood vessels in the lungs to allow blood to flow easily.

(from medlineplus.gov)

"Sildenafil citrate, sold under the names Viagra, Revatio and under various other names, is a drug used to treat male erectile dysfunction (impotence) and pulmonary arterial hypertension (PAH), developed by the pharmaceutical company Pfizer. Its primary competitors on the market are tadalafil (Cialis), and vardenafil (Levitra)."

"6 Other uses
6.1 Pulmonary hypertension
6.2 Raynaud's phenomenon
6.3 Altitude sickness
6.4 Duchenne/Becker Muscular Dystrophy
7 Non-medical use
7.1 Aphrodisiac
7.2 Recreational use
7.3 Prevention of plant wilting
7.4 Jet lag research "

"The 2007 Ig Nobel Prize in Aviation went to Patricia V. Agostino, Santiago A. Plano and Diego A. Golombek of Universidad Nacional de Quilmes, Argentina, for their discovery that Viagra aids jet lag recovery in hamsters. Their research was published in the Proceedings of the National Academy of Sciences."
Source and further information:
http://en.wikipedia.org/wiki/Viagra

For implying the direction the one with the erection should follow