A standard data acquisition according to Einthoven or Goldberger is used and transmitted to a pre-amplifier and data are transferred to a computer. The ECG-signal is digitalized with a frequency of 500 Hz (12 bit resolution) and monitored continuously on the screen. The R-spike recognition process contains an ?envelope-curve-technology“ making sure a constant recognition of the signal even in the presence of disturbance by strong low frequency waves. For permanent control recognized R-spikes are actually marked on-line on the screen and are presented as heart beat rate values. Additionally acoustical verification can be activated in parallel. The duration of the last R-R interval recognized together with the mean heart beat rate over the last 20 heart beats is shown on the screen. A monitoring diagram - relating heart beat rate and time – unveils the actual variability of the R-R intervals during the data acquisition process.