In the three species, heparin at 100 IU/ml effectively inhibited collagen-induced platelet aggregation (A), but had a very weak effect on inhibiting aggregation induced by ristocetin (B) and ADP (C). Heparin at 1, 10 and 100 IU/ml equally and effectively inhibited thrombin-induced platelet aggregation (D). Values of mean percentage (%) of aggregation are indicated in the figure. (*p<0.05, **p<0.01, ***p<0.001).