The invention relates to a method for checking ECG signals measured by an ECG measuring device having at least three electrodes for the presence of interference errors. At least three voltages are measured on a closed circulation path across the electrodes of the ECG measuring device. A monitoring value is calculated from the three measured voltages. A presence of an error is checked by determining a deviation of the monitoring value from a reference value. An error signal is outputted if an error is presented. The ECG measuring device has a further processing unit for processing voltage signals between a different pair of electrodes and a monitoring unit for calculating the monitoring value.