A single-chamber cardiac stimulator (10) with at least partially electrically conductive housing (12) and first detection unit (52) connected via a ventricular electrode line to at least one ventricular electrode and another electrode and configured to record ventricular cardiac activity with first electrocardiogram signal via the ventricular electrode and additional electrode, comprises a second detection unit (70), connected via the ventricular electrode line to at least one electrode of the ventricular electrode line and is connected to another electrode and configured to record a second electrocardiogram signal simultaneously with the first electrocardiogram signal via these electrodes, such that at least one of the two electrodes by means of which the second electrocardiogram signal is to be recorded is another electrode by means of which the first electrocardiogram signal is to be recorded, so that the electrocardiogram signals form ECG leads whose vectors are not equal to 0° or 180°.
