Chocolate is made from plants, which means it contains many of the health benefits of dark vegetables. These benefits are from flavonoids, which act as antioxidants.

Antioxidants protect the body from aging caused by free radicals, which can cause damage that leads to heart disease. Dark chocolate contains a large number of antioxidants (nearly 8 times the number found in strawberries). Flavonoids also help relax blood pressure through the production of nitric oxide, and balance certain hormones in the body.

Source: About.com