Scanning of all of the Holter recordings shown in the figures was carefully verified. Revisiting the series of plots shown for the different subjects, it becomes clear that some subjects have normally configured plots by every test. In those subjects, traditional time or frequency domain HRV, whether high or low, can be calculated and should reflect cardiac autonomic function. Although, with experience, direct visualization of the HR tachogram provides an excellent starting point, a set of 24 hourly Poincaré plots and FFTs, each printed on a single page, provide a rapid way to assess each continuous electrocardiogram recording, and those that are normally organized by FFT and Poincaré plot criteria can generally be accepted for HRV analysis. The question of what to do with abnormal plots is complex and is the subject of ongoing investigations. At a minimum, the Holter scanning should be verified to ensure that the irregular rhythm is not due to undetected ectopy or nonuniform detection of beat onsets. If, however, this rhythm is truly present, as mentioned, circadian HRV measures, calculation of VLF power, and nonlinear methods can still be applied to characterize HRV for research studies. Short-term measures are meaningless in these cases, expect that when they appear to be unusually high relative to total HRV or to the population being studied, they are a red flag for erratic rhythm.