The ryanodine receptor (RyR) family is a class of intracellular calcium channel that is responsible for mediating the calcium efflux from the endoplasmic reticulum (ER; or in muscle the sarcoplasmic reticulum, SR). Upon activation, the RyR produces an elevation in cytoplasmic free calcium that can trigger numerous calcium-activated physiological pathways in a variety of cells. The RyR is the largest known membrane protein and exists as three distinct isoforms (RyR1, 2, and 3) each formed by four identical subunits of approximately 5000 amino acids with a molecular mass of 560,000 Daltons, culminating in a ~2.3 megadalton complex. Electron microscopy of the purified complex has indicated the protein resembles a mushroom shape, with the stalk, or transmembrane domain, constituting 10-20% of the molecule, a region that is predicted to be at the C-terminal end. The opening and closing of the intrinsic calcium efflux pathway within the RyR is regulated by many physiological (e.g. calcium, magnesium, adenine nucleotides, pH and redox) and pharmacological (e.g. ryanodine, caffeine, tetracaine, neomycin, ruthenium red) effectors, as well as by a diverse array of cytoplasmic (e.g. FKBP12, calmodulin), lumenal (e.g. calsequestrin) and integral SR membrane (e.g. triadin, neighbouring RyRs) proteins. The most studied physiological process involving the RyR is that of excitation-contraction coupling in striated muscle, where plasma membrane excitation is transmitted to the cell interior and results in RyR-mediated calcium efflux to trigger myocyte contraction. Mutations in the skeletal muscle RyR (RyR1) are known to be responsible for the clinical syndromes of malignant hyperthermia and central core disease, which are thought to be mediated by aberrant SR calcium release due to dysfunctional RyR1. Recently, single residue mutations in the RyR2 have also been identified in families that exhibit catecholaminergic polymorphic ventricular tachycardia (CPVT), a condition in which physical or emotional stress can trigger severe tachyarrhythmias that can lead to sudden cardiac death. The mutations in RyR2, which currently number over 60, are distributed throughout the linear RyR2 sequence, although clustering of mutations appears to occur in the N- and C-terminal domains, as well as in a central domain of the RyR2. Further, a critical signalling role for dysfunctional RyR2 has also been implicated in the generation of arrhythmias in the common condition of heart failure. We have prepared a cDNA expression plasmid encoding the 15 kilobase human cardiac RyR2 and have introduced various reported mutations into this construct to enable mammalian cell expression and analysis of dysfunctional calcium release mediated by the wild type and mutated RyR2. These studies suggest that the mutational locus may be important in the mechanism of calcium channel dysfunction. Understanding the causes of aberrant calcium release via RyR2 may assist in the development of effective treatments for the ventricular arrhythmias that often leads to sudden death in heart failure and in CPVT.