Fig. 6. Haemodynamic effects of blood volume alterations in South American rattlesnakes Crotalus durissus, as a function of mean circulatory filling pressure (MCFP) measured at each blood volume change. (A) VS_pul, pulmonary stroke volume; (B) VS_sys, systemic stroke volume; (C) VS_tot, total stroke volume; (D) _pul/_sys, ratio of pulmonary cardiac output to systemic cardiac output; (E) R_sys, systemic resistance; (F) R_ven, venous resistance. Black symbols represent the untreated group and grey symbols represent the -blocked group. Triangles indicate control values at normal blood volume. Values are means ± S.E.M. (N=6 for each group). * indicates a significant difference relative to control value. indicates a significant difference between the two groups of snakes. (1 cm H₂O=0.098 kPa.)