Equinatoxin II (EqT II) is a basic, cardiotoxic polypeptide. The vasoconstrictory effect of the toxin on isolated porcine coronary arteries was diminished by nicardipine, an L-type calcium channel antagonist. A comparison was made of the effects of EqT II alone and EqT II in the presence of nicardipine on the coronary flow in porcine and rat hearts isolated according to Langendorff's method. In both models EqT II decreased coronary flow in a dose-dependent manner and there were no statistically significant differences between the two models (p>0.05). However, 1 M nicardipine diminished the effects of EqT II on coronary flow in isolated porcine hearts more than in isolated rat hearts (p<0.05). The results suggest that the activation of L-type calcium channels is one of the mechanisms involved in the lowering of coronary flow induced by EqT II.