I'm currently using Kubios for HRV analysis but it's limited in analysis of recordings lesser than 10 beats. Just wondering if someone has used any other software for recordings shorter than 10 beats?
You can try a HRV analysis tool created by Marcus Vollmer in MATLAB (https://www.mathworks.com/matlabcentral/fileexchange/52787-marcusvollmer-hrv). Changing the code will let you set whatever window size you want.