Chronic heart failure is a common, disabling disorder with high mortality, which is mainly attributable to left ventricular systolic dysfunction. Oxidative stress may have both functional and structural effects on the myocardium, leading to myocardial decompensation. In this study we examined oxidative stress in patients with varying degrees of heart failure. Methods Fifty one patients with chronic heart failure and 31 control subjects were studied. Complete clinical and echocardiographic evaluations were done. The functional capacity of patients were determined. Oxidative stress were evaluated by measuring plasma malondialdehyde, vitamin E and β-caroten levels. Results: The distribution of age, cause of heart failure and drug intake were not significantly different among the different classes of heart failure. The malondialdehyde levels were significantly different between control subjects and patients with chronic heart failure (p<0.01). There was a significant positive correlation between the patients' malondialdehyde levels and functional class (r=0.59, p<0.0001). There was a negative correlation between the functional class and vitamin E and β-caroten levels (r=-0.43, p<0.0001 and r=-0.25, p<0.01 respectively). Conclusion: These data demonstrate that oxidative stress is increased systemically in patients with chronic heart failure. This increase correlates with functional class.