In this contribution, we will discuss the possibilities that PPGI can bring if we move from the central oscillator (the heart) to the slow rhythms occurring in tissue perfusion, referred to as perfusion clouds. Thus, changes in perfusion are also characterized by other components that fall in the frequency domain below the heart rate (HR). Here we can generally classify oscillations in: high frequency (HF, in the range 0.18 Hz - 0.4(0.6) Hz), intermediate (IM, 0.12 Hz - 0.18 Hz), low frequency (LF, 0.05 Hz - 0.12 Hz), and very low frequency (VLF, below 0.05 Hz) band. Each frequency band is related to a different physiological process. For example, respiration and blood volume changes in the venous system are contained in the HF band. The IM and LF band can be characterized by myogenic activity of the arteriolar smooth muscle and neurogenic activity, with IM reflecting regulation of the ANS via efferent vagal activity and LF involving sympathetic activity with possible vagal modulation. The VLF region is characterized by endothelial nitric oxide (NO)-dependent processes at the upper VLF band (0.01 Hz - 0.05 Hz) and NO-independent processes at the lower VLF band (0.005 Hz - 0.01 Hz). In addition, the perfusion oscillations in the region below HR show one more interesting feature that is the subject of current studies, namely their spatial amplitude and phase (synchronization) inhomogeneity. Research in this area reveals an interesting phenomenon and that is the synchronization of these vasomotor rhythms during external stimulation of the organism, e.g. by the cold pressor test. Tissue perfusion is thus a rich source of information not only about cardiac activity but also about other important processes taking place in the organism.