Acute effects of aflatoxins (AF), and in particular cardiac actions, have not been examined as much as chronic toxicity. Thus, in the present study we evaluated the effects of specific AF on isolated guinea pig atria. Isoprenaline (ISO, 4x10(-9)), AFB(1) (3x10(-6) and 6x10(-5) M) and AFG(1) (3x10(-6) and 6x10(-6) M) contracted the isolated guinea pig atria, leaving the preparation hyperresponsive to ISO. These properties of AF are of interest as they could be responsible of certain cardiotoxic effects described in the literature.