Cardiac Ca²⁺ transients are enhanced by cAMP‐dependent protein kinase (PKA). However, PKA‐dependent modulation of ryanodine receptor (RyR) function in intact cells is difficult to measure, because PKA simultaneously increases Ca²⁺ current (I_Ca), SR Ca²⁺ uptake and SR Ca²⁺ loading (which independently increase SR Ca²⁺ release). We measured I_Ca and SR Ca²⁺ release ± 1 μm isoproterenol (ISO; isoprenaline) in voltage‐clamped ventricular myocytes of rabbits and transgenic mice (expressing only non‐phosphorylatable phospholamban). This mouse model helps control for any effect of ISO‐enhanced SR uptake on observed release, but the two species produced essentially identical results. SR Ca²⁺ load and I_Ca were adjusted by conditioning. We thus evaluated PKA effects on SR Ca²⁺ release at constant SR Ca²⁺ load and I_Ca trigger (with constant unitary I_Ca). The amount of SR Ca²⁺ release increased as a function of either I_Ca or SR Ca²⁺ load, but ISO did not alter the relationships (measured as gain or fractional release). This was true over a wide range of SR Ca²⁺ load and I_Ca. However, the maximal rate of SR Ca²⁺ release was ∼50% faster with ISO (at most loads and I_Ca levels). We conclude that the isolated effect of PKA on SR Ca²⁺ release is an increase in maximal rate of release and faster turn‐off of release (such that integrated SR Ca²⁺ release is unchanged). The increased amount of SR Ca²⁺ release normally seen with ISO depends primarily on increased I_Ca trigger and SR Ca²⁺ load, whereas faster release kinetics may be the main result of RyR phosphorylation.