Resveratrol is a known antioxidant found in wine, berries, and peanuts and is credited with a protective effect on the human body. Its biosynthesis is induced by stressful conditions such as pathogen attacks and UV radiation. In this master's thesis, the plasma concentration of resveratrol in cardiovascular patients scheduled for surgery, who took a total of 800 mg of resveratrol or placebo per day via twice a day capsules, was measured by high performance liquid chromatography (HPLC). Blood was sampled during and after surgery. Also, in both plasma samples of patients who were receiving resveratrol, and in control samples, plasma antioxidant capacity was measured spectrophotometrically by the FRAP method. The measured resveratrol concentration was low in relation to the received dose, which indicated the low bioavailability of resveratrol due to its extensive metabolism. The obtained high coefficients of variation of resveratrol concentration indicated differences among the subjects in the composition of the intestinal microbiota, genetic polymorphism in enzymes of phase II metabolism, and circadian rhythm. The plasma antioxidant capacity showed a statistically positive correlation with resveratrol concentration. However, plasma antioxidant capacity after surgery was statistically lower in plasma samples of people treated with resveratrol compared to those treated with a placebo. This indicated nonspecificity of the FRAP method. Therefore, for a more complete insight into the effect of resveratrol on antioxidant capacity, other methods of measuring antioxidant activity should be used.