Much of the protection against cardiovascular disease attributed to wine intake may relate not only to the alcohol, but to its polyphenolic constituents.  This review article summarises research into the chemistry, bioavailability, metabolism and excretion of polyphenols as well as mechanisms of their action.  As stated by the authors, ‘These protective effects could be due to one or many components of the complex mixture of bioavailable and bioactive compounds present in red wine including ethanol, resveratrol, flavonols, flavan-3-ols, anthocyanins, phenolic acids as well as their metabolites formed either in the tissues or in the colon by the microflora.’ 
The authors describe their cardioprotective effects, effects on vascular function and atherosclerosis, anti-platelet effects, effects on myocardial ischemia, and anti cancer and anti-diabetic effects.
The authors conclude that ‘Polyphenols are the most abundant antioxidants in the diet and are widespread constituents of wine, fruits and vegetables.’  Their review provides an extensive scientific literature on polyphenols in wine; it suggests multiple mechanisms by which such substances may have beneficial effects on health.
Reference:  Rodrigo R, Miranda A, Vergara L.  Modulation of endogenous antioxidant system by wine polyphenols in human disease.  Clin Chim Acta 2011;412:410-424