Fig. 4. The change in maximum cardiac output (A) and maximum cardiac power output (B) of perfused rainbow trout hearts at 10°C under hypoxic, hyperkalemic (5 mmol l^–1), acidotic (pH 7.5) perfusate with both tonic (5 nmol l^–1) and maximal (500 nmol l^–1) adrenergic stimulation. Individual groups of hearts were exposed to specific hypoxia levels as indicated on the x-axis, and results are shown from several series of experiments, each indicated as a separate line segment. The series were as follows. Series III: 12.6 kPa (N=6), 10 kPa (N=10), 6.7 kPa (N=6), series IV: 5.0 kPa (N=7), 3.3 kPa (N=8), 2.7 kPa (N=5), and series V: 2.7 kPa (N=6), 2.0 kPa (N=6) and 1.3 kPa (N=4). Values are reported as percent change from an original assessment under normoxic conditions. One-way repeated-measures ANOVA and Holm–Sidak multiple comparisons tests were used to compare treatment means and each heart acted as its own control. Values shown are means ± s.e.m. *Significant difference from normoxia (P=0.05).