  The heart rate variability (HRV) in diabetic human subjects, has been
analyzed using lagged Poincar\'{e} plot, auto-correlation and the detrended
fluctuation analysis methods. The parameters $SD1$, and $SD12 (= SD1/SD2)$ for
Poincar\'{e} plot for diabetic are lower than that for non-diabetic subjects
and reverse is case for $SD2$ for all lagged number (m). The slope and the
curvature of the plot SD12 vs m is much reduced for diabetic subject. The
scatter plot of two successive interbeat intervals points out smaller
variability in diabetic heart. The detrended fluctuation exponent has a higher
value for diabetic group. The auto-correlation function of the deviation of
interbeat interval in diabetic group shows highly correlated pattern when
compared to that of normal one. The study suggests that the curvature of $SD12$
and auto-correlation method appear to be better way to assess the alteration of
regulatory system on heart dynamics in diabetic condition.
