Fig. 2. Effects of external [Ca²⁺] on cardiac parameters recorded from spontaneously beating yellowfin tuna hearts in situ at 20°C. Data shown are for standard conditions (Heart rate), maximum flow (Stroke volume, Cardiac output) and maximum power (Power). Values are means + S.D. N=4. An asterisk indicates a value significantly different from the value at 1.8 mmol l^-1 Ca²⁺. A dagger indicates a value significantly different from the value at 3.7 mmol l^-1 Ca²⁺.