Grape Seed Extract contains oligomeric proanthocyanidins (OPCs). They are flavonoid-rich compounds with very potent antioxidant properties. OPCs have been found to inhibit lipid peroxidation, and to affect enzyme systems including phospholipase A2, xanthine oxidase, cycloxygenase, and lipoxygenase. OPCs help maintain capillary strength and integrity and venous tone.