The novel RYR2-S4153R mutation has been implicated as a cause of CPVT and atrial fibrillation. The mutation has been functionally characterized via store-overload-induced Ca(2+) release (SOICR) and tritium-labelled ryanodine ([(3)H]ryanodine) binding assays. The S4153R mutation enhanced propensity for spontaneous Ca(2+) release and reduced SOICR threshold but did not alter Ca(2+) activation of [(3)H]ryanodine binding, a common feature of other CPVT gain-of-function RYR2 mutations. We conclude that the S4153R mutation is a gain-of-function RYR2 mutation associated with a clinical phenotype characterized by both CPVT and atrial fibrillation.