We have investigated the cardiotoxic effect of Bothrops jararacussu crude venom and the ability of suramin to antagonize this effect in the heart of rats, as well as the proteolytic and phospholipase A(2) (PLA(2)) venom activities. Continuous perfusion in an isolated heart of a rat on a Langendorff preparation with a Ringer's solution with B. jararacussu crude venom (2.5-10.0 microg/mL) induces stoppage and a decrease in the cardiac tension, which were time- and concentration dependent. The analysis of the heart perfusate solution showed an increase in the rate of creatine kinase induced by the venom. Pre-incubation with suramin (1.0-30.0 microM) protected against the venom cardiotoxic effect in a concentration-dependent way, reaching up to 90% with 30.0 microM, and prevent the heart stoppage and decrease the tension. These protective effects were increased by the association with polyvalent antibothropic antivenom, suggesting a synergic effect. The PLA(2) and proteolytic activities of B. jararacussu crude venom were also inhibited in a concentration-dependent way by suramin, showing that this polyanion antivenom activity has therapeutic potential to be used as an antivenom.