CLOCK and hydrops fetalis: The strong positive correlations of the rates at which HF components of RR intervals within the time series decreased between 21 and 30 months in each mouse and the rates at which SD1:SD2 decreased in that mouse suggest that reductions in the kinetics of pacemaker cell clock functions and desynchronization among these functions [5] may be linked to increased nonlinearity of RR interval variability within both the short- (SD1) and long-term (SD2) RR interval correlations buried within the EKG RR interval time series.