HRV is typically performed on ECG recordings ranging in length from as short as 5mins to >24hours. The consecutive beat-t-beat intervals (R-R intervals) are extracted from the ECG. Since its the variations in time between normal heartbeats (N-N intervals) that is analyzed, it is essential that abnormal beats (such as ectopics and noise) are removed from the analysis. The HRV module in LabChart can automate this process for you.