Tunas are capable of exceptionally high maximum metabolic rates, which requires rapid delivery of oxygen and metabolic substrate to the tissues. This requirement is met, in part, by exceptionally high maximum cardiac outputs, opening the possibility that myocardial Ca²⁺ delivery is enhanced in tuna myocytes compared with other fish. In this study, we investigated the electrophysiological properties of the cardiac L-type Ca²⁺ channel current (I_Ca) to test the hypothesis that Ca²⁺ influx would be larger and have faster kinetics in cardiomyocytes from Pacific bluefin tuna (Thunnus orientalis) compared with those of its sister taxa, the Pacific mackerel (Scomber japonicus). In accordance with this hypothesis, I_Ca in atrial myocytes from bluefin tuna had significantly greater peak current amplitudes and faster fast inactivation kinetics (-4.4±0.2 pA pF^-1 and 25.9±1.6 ms, respectively) compared with mackerel (-2.7±0.5 pA pF^-1 and 32.3±3.8 ms, respectively). Steady-state activation, inactivation and recovery from inactivation were also faster in atrial myocytes from tuna compared with mackerel. In ventricular myocytes, current amplitude and activation and inactivation rates were similar in both species but elevated compared with those of other teleosts (47). These results indicate enhanced I_Ca in atrial myocytes from bluefin tuna compared with Pacific mackerel, which may be associated with elevated cardiac performance because I_Ca delivers the majority of Ca²⁺ involved in excitation-contraction coupling in most fish hearts. Similarly, I_Ca is enhanced in the ventricle of both species in comparison with other teleosts and may play a role in the robust cardiac performance of fishes of the family Scombridae.