Fig. 2. (A) Lactate dehydrogenase (LDH) and (B) citrate synthase (CS) activities at 20°C in shark heart ventricle (HV; an unknown mixture of compact and spongy myocardium). Values are means ±S.E.M. for ectothermic sharks (open bars) and sharks known to be endothermic (shaded bars). Values in parentheses at the base of each bar are the sample size and the data source: a, present study; b, Dickson et al. (1993). Horizontal lines group species that do not differ significantly from the comparison species (indicated by a black circle), as determined by a Tukey—Kramer multiple comparisons test at P<0.05. For example, leopard shark HV CS (bottom horizontal line in B) is not significantly different from that of the blue shark but differs significantly from all other species studied.