Fig. 2. Cumulative concentration-response curve showing the effect of L-arginine (L-Arg; from 10^–7 to 10^–5 mol l^–1) on stroke volume (VS) and stroke work (WS) in isolated and perfused icefish hearts. Percentage changes were evaluated as means ± S.E.M. of five experiments. Asterisks indicate values significantly different from the control value: ^*P<0.05, ^**P<0.025.