RYR2 and catecholaminergic polymorphic ventricular tachycardia: Furthermore, we hypothesized that differences in RyR2 activity (i.e., lower activity in healthy rat myocytes compared to CPVT myocytes) determine the potency of open-state RyR2 blockers such as FLEC against Ca2+ waves in cardiomyocytes and could help explain the differences between our results and that of other groups.