Portable system for the measurement of heart rate

We describe a simple RR interval recording system; it does not involve an analogue recording of ECG data on magnetic tape and does not therefore suffer from the inherent problem of tape speed variability on playback, which is a frequent cause of inaccuracies in RR interval timing. The system operates in both recording and playback modes and records of up to 60 minutes duration can be obtained without operator intervention. Its accuracy with respect to RR interval is not less than 99.5%.