The complex dynamics of the autonomic nervous system manifests in the random fluctuation of the sinus rhythm. Recent results on multiple scaling and multifractal in HRV indicate intricate details beyond the second order statistics (such as the power spectrum) of the interbeat interval data (RRi). In this work, the notions of structure function and cascade from fully developed turbulence (FDT) are used to examine and model the scaling property of the long-term, daytime, RRi fluctuation from healthy humans. Our conclusions are the qualitative as well as quantitative similarities between the statistics of daytime RRi and the velocity increment in FDT and the possibility to model such similarities by using a cascade generating mechanism.