Salt-sensitive rats fed a high-salt diet and a powdered mix of table grapes (which contain flavonoids, which are antioxidants) achieved improvements in blood pressure control and experienced cardioprotective effects, according to studies by scientists at the University of Michigan in Ann Arbor (Seymour EM. J Gerontol A Biol Sci Med Sci. 2008;63:1034-1042).
Two groups of rats were fed a high-salt diet, with or without grape powder (the equivalent of 9 servings of grapes daily). Two other groups were fed a low-salt diet, with or without grape powder. After 18 weeks, among rats on the high-salt diet, those given grape powder had lower blood pressure, better heart muscle function and structure, and lower markers of inflammation than those that did not receive the grape powder; those in the low-salt diet group that were given grape powder had a similar improvement in heart muscle structure and had molecular indicators of less cardiac stress.
Hildreth CJ. Grapes and Heart Failure. JAMA. 2009;301(1):26. doi:10.1001/jama.2008.925