Fig. 1. Dose–response relation of protamine-induced percent changes in mean arterial pressure, heart rate, cardiac output, and systemic vascular resistance at 1 and 5 min after protamine injection in six conscious dogs (open squares) and the effects of heparin on the protamine-induced changes (closed circles). Data are presented as mean ± SEM. * P < 0.05 compared with the value obtained in the experiments without heparin at each concentration. †P < 0.05 compared with the control value within each group. iv = intravenous.