A novel cardiotoxic polypeptide from the venom of Atractaspis engaddensis (burrowing asp): cardiac effects in mice and isolated rat and human heart preparations. Toxicon 26, 525 - 534, 1988. - A new cardiotoxic polypeptide isolated from the venom of the snake Atractaspis engaddensis has an LD50 of 15 μg/kg body weight in white mice. Intravenous administration in mice of lethal doses of the toxin causes, within seconds, marked changes in the ECG, consisting primarily of a transient slope elevation of the S-T segment, a temporary diminution of the S-wave and an increase in the amplitudes of the R- and T-waves. Concomitantly, and apparently unrelated to these changes, a severe A-V block develops and leads to complete cardiac arrest within a few min. Studies with rat and human isolated heart preparations showed that the toxin exerts a powerful coronary vasoconstriction (rats), and positive inotropic effects (rats and humans).