What factors does garlic have which causes high blood pressure and tension to decrease?

I’m very much interested in knowing the factors or components of garlic which causes high blood pressure and tension to effectively decrease only a few minutes after taking it. I would also like to know the benefits and disadvantages that the biochemical components of garlic has for the heart.
What are the nutrients in garlic that the heart accommodates for it to help decrease blood pressure and tension??

Try this site:

http://altmedicine.about.com/cs/herbsvitaminsek/a/Hypertension.htm