The study of heart rate variability (HRV) provides a mean for observing the heart's ability to respond to normal regulatory signals that affect its rhythm. The HRV analysis has proven useful in diagnosis, treatment and monitoring of various pathologies. The modern field of HRV processing is extremely diverse, involving many areas like spectral estimation, system modeling, nonlinear dynamics and chaotic analysis, etc. Thus, there is an urgent need to keep a track of recent advancements and activities taking place in this emerging.field. Moreover, the development of chaos theory in the last decades supplied the framework to study the complex dynamics, of heart rate, through a new approach. Many efforts were made to explain the complex behavior of deterministic systems with the presence of nonlinear features instead of the usual stochastic models. In the second of two articles on signal processing for HRV, we explore the HRV using time frequency and non-linear analysis approaches.