The analysis of heart rate variability (HRV) has received increasing attention, particularly since the widespread introduction of 24 hour monitoring procedures. This paper compares methods for obtaining the HRV signal in both real time and 60 x real time. Software and hardware methods are compared from a number of points of view including accuracy and suitability for analysing 24 hour recordings. The question of drop-outs resulting from noisy ECG records is discussed and one hardware method for minimizing the problem is described which uses a level restorer in conjunction with the HRV signal generator.