Resveratrol is a controversial supplement. Some researchers say it is worthless and others are very vocal about the benefits to general longevity.
It works it seems by stimulating our adult stem cells or progenitor cells. These cells attach to the walls of blood vessels, helping to regenerate and heal them. People with heart disease, diabetes and high blood pressure have lower levels of these progenitor cells.
Another benefit to overall longevity is Resveratrol activates telomerase which can repair/rebuild telomeres.
Dr Al Sears discusses here talks about one particular study and how resveratrol might work.