o further understand the mechanism of action, we tested the hypothesis that cardiac glycosides affect ryanodine binding to ryanodine type 2 (RyR2) receptors. It has been proposed that RyR2 has a binding site for cardiac glycosides. This binding activates the RyR2 channel directly, resulting in an increased release of calcium through the sarcoplasmin reticulum. Our results indicate that the cardiac glycosides, oleandrin or ouabain, do not directly affect the binding of Ry to RyR2.