Fig. 3. Effects of bolus injections (2 and 10 µg kg^-1) of adrenaline, phenylephrine and isoproterenol on haemodynamic variables in anaesthetised South American rattlesnakes Crotalus durissus: (A) _tot, total cardiac output; (B) _pul/_sys, ratio of pulmonary cardiac output to systemic cardiac output; (C) VS_sys, systemic stroke volume; (D) VS_tot, total stroke volume; (E) R_sys, systemic resistance; (F) R_ven, venous resistance. Black bars represent control values. Grey bars represent values after injection of the various adrenergic agonists. Values are means ± S.E.M. (N=6). Asterisks indicate a significant difference relative to control values. (1 cm H₂O=0.098 kPa.)