Modulation of the ryanodine receptor primarily controls sarcoplasmic reticulum calcium content rather than cytoplasmic calcium concentration, indicating it does not have a maintained effect on cardiac contraction.
Cardiac contraction is initiated by Ca(2+) leaving the sarcoplasmic reticulum through the ryanodine receptor (RyR). Although opening of the RyR can be modified by various ligands, these have no maintained effect on contraction. We conclude that modulation of the RyR controls sarcoplasmic reticulum Ca(2+) content rather than cytoplasmic Ca(2+) concentration.
Eisner et al. (Sun,) studied this question.