Type 2 ryanodine receptors (RyR2s) are the calcium release channels of sarcoplasmic reticulum (SR) that provide the majority of calcium ions (Ca2+) necessary to induce contraction of cardiac cells.In their intracellular environment, RyRs are regulated by a variety of cytosolic and luminal factors so that their output signal (Ca2+) induces finely-graded cell contraction without igniting cellular processes that may lead to aberrant electrical activity (ventricular arrhythmias).