Chronic heart failure (CHF) involves interactions between the cardiovascular, neuroendocrine and immune systems. This study investigated the seropositivity rate for anti-Toxoplasma IgG and IgM antibodies by ELISA in patients with CHF. Ninety-seven patients with CHF and 50 healthy volunteers were selected for this investigation. The seropositivity rate for anti-Toxoplasma IgG antibodies among CHF patients (68%) was significantly higher than in healthy volunteers (36%). Thus, parasitological screening of this group of patients should be periodically performed to prevent the possible dissemination of toxoplasmosis.