To separate RyR leak from the complex HF phenotype, in terms of the arrhythmogenic feedback signalling network (i.e., the vicious cycle), we induced RyR leak by low [caffeine] (200 μmol/L) and isoproterenol (ISO; 100 nmol/L) in healthy rabbit ventricular myocytes. Here, RYR2 is linked to hydrops fetalis.