Malondialdehyde (MDA), a marker of lipid peroxidation, was measured in the plasma of patients with congestive heart failure (CHF) having varying degrees of clinical symptoms and in control subjects. The 53 patients studied were divided in two groups based on their left ventricular ejection fraction (LVEF). Group A consisted of 30 symptomatic patients with chronic CHF (NYHA classes II and III) and LVEF < 40%. Group B consisted of 23 asymptomatic patients with LVEF > 40%. Patients in group A (mean LVEF = 28) has a significantly greater history of myocardial infarction (88% vs 48%; p = 0.002) than those in group B. Group B patients and the controls had similar LVEFs (58.0 vs 62.1; p = 0.14). Neither patients in the CHF group nor group B patients showed correlation between MDA values and LVEF, unless control were included. Mean MDA concentrations in groups A (2.65 +/- 1.03 mumol/L) and B (2.1 +/- 0.7 mumol/L) were significantly higher than those in the control group (1.45 +/- 0.77 mumol/L; p < 0.05), supporting the hypothesis that the CHF state and underlying risk conditions appear to be associate with abnormal oxidative stress. Moreover, a significant correlation (r = 0.74; p = 0.0001) was found in group A patients between the MDA values and the duration in years (chronicity) of the CHF state.