Heart rate variability (HRV) refers to beat to beat variation in heart rate (R-R intervals) of electrocardiogram (ECG) that quantifies the interplay between sympathetic and parasympathetic activity of autonomic nervous system (ANS). HRV parameters can be categorized in time domain, frequency domain, time-frequency and non-linear methods. Commercially available ECG acquisition equipment does not usually include HRV functionalities due to the lack of standard diagnostic protocols. As an alternative to commercial softwares, many simple, online free, device-independent and portable software tools are developed for HRV analysis and cardiovascular research. This paper briefly reviews the state of the art in the field of HRV analysis softwares. Features of various freely available HRV analysis tools are described in depth.
