Grape seed proanthocyanidin extract (GSPE) is a popular dietary supplement that has been shown to have a wide variety of beneficial actions. First brought into public consciousness as one of the key active components of red wine, proanthocyanidins are bioavailable in plasma and have potent antioxidant activity. Their free radical scavenging properties are greater than popular antioxidants such as vitamins C and E, and GSPE shows a superior ability to protect cells against lipid peroxidation and DNA fragmentation. GSPE also exhibits cardioprotective effects by preserving myocardial function after ischemia and reperfusion, and reduces total cholesterol levels in combination with the anti-aging supplement chromium polynicotinate through a synergistic effect. GSPE has been shown to inhibit the growth of cancer cells, while encouraging growth in normal human cells and protecting normal human cells against the toxicity of chemotherapeutic agents. Proposed mechanisms for GSPE's activity towards cancer cells include GSPE-modulated upregulation of bcl-Xs and JNK genes leading to apoptosis, as well as downregulation of bcl-Xl expression and mitogenic signaling to promote cell growth. Toxicity and mutation studies have demonstrated the safety of GSPE, supporting the use of GSPE as a health supplement.