A device for detecting the state of a heart on the basis of intracardial impedance measurement. The device has an impedance measuring unit, which has electrical terminals, configured to be electrically connected or to be connected to electrodes for delivering and detecting a current or voltage, and is implemented to ascertain an impedance on the basis of the dimension of the delivered current or voltage and the voltage drop caused by the current or the current caused by the voltage, as well as an analysis unit, which is connected to the impedance measuring unit and is implemented to derive a cardiac function parameter from a time curve of the impedance ascertained using the impedance measuring unit. The analysis unit analyzes the impedance curve assigned to a diastole and derives a cardiac function parameter characterizing the behavior of a heart during the diastole (filling phase of the ventricle).