Fig. 1. The effects of hyperkalemia on maximum cardiac output (A) and maximum cardiac power output (B) of perfused rainbow trout hearts at 10°C, pH 7.9. Values are reported as mean ± s.e.m. Individual hearts (N=9) were exposed to the following sequence of perfusates: (1) control (normoxia), (2) 5 mmol l^–1 K⁺, (3) 7.5 mmol l^–1 K⁺, (4) control (recovery) and (5) 7.5 mmol l^–1 K⁺ with 500 nmol l^–1 adrenaline (AD). Repeated measures one-way ANOVA and a Holm-Sidak multiple comparisons test were used to compare treatment means. Different letters denote significant differences at P=0.05.