Fig. 4. Decreases in (A) cardiac output and (B) heart rate fH during 10 min (triangles; N=7), 20 min (open circles; N=7) and 30 min (filled circles; N=8) of severe hypoxia. Repeated-measures ANOVA showed that there were no significant differences between the treatments. Data for control fish are not shown because these hearts were not exposed to severe hypoxia, and was maintained at 16–17 ml min^–1 kg^–1.