Apparatus for cardiac monitoring of a patient, in particular of a patient in cardiorespiratory arrest during cardiopulmonary resuscitation, comprising: - means (4, 8, 9) for measuring the cardiac activity of the patient, - at least one graphical user interface, - means for measuring the CO 2 content in order to perform measurements of the concentration of CO 2 produced by said patient and to supply CO 2 content measurement signals to signal-processing means, - signal-processing means configured to process the CO 2 content measurement signals originating from the CO 2 content measurement means, and - storage means for recording at least the CO 2 values processed, characterized in that: A) the signal-processing means are configured to: i) select a maximum CO 2 content value (Vmax) from a plurality of CO 2 content values measured during a given time period (dt) and recorded in the storage means, ii) repeat step i) in order to obtain several successive maximum CO 2 content values (Vmax) measured over a time window (Ft) comprising several successive time periods (dt), iii) calculate at least one mean CO 2 content value (Vmean) from the maximum CO 2 content values (Vmax) obtained over the time window (Ft), iv) repeat steps i) to iii) in order to obtain several successive mean CO 2 content values (Vmean) calculated from maximum CO 2 content values (Vmax) obtained over several successive time windows (Ft), and v) transmit the mean CO 2 content values (Vmean) to the graphical user interface, and B) the graphical user interface is configured to display the mean CO 2 content values (Vmean) in the form of at least one graphical representation. - means (4, 8, 9) for measuring the cardiac activity of the patient, - at least one graphical user interface, - means for measuring the CO 2 content in order to perform measurements of the concentration of CO 2 produced by said patient and to supply CO 2 content measurement signals to signal-processing means, - signal-processing means configured to process the CO 2 content measurement signals originating from the CO 2 content measurement means, and - storage means for recording at least the CO 2 values processed, A) the signal-processing means are configured to: i) select a maximum CO 2 content value (Vmax) from a plurality of CO 2 content values measured during a given time period (dt) and recorded in the storage means, ii) repeat step i) in order to obtain several successive maximum CO 2 content values (Vmax) measured over a time window (Ft) comprising several successive time periods (dt), iii) calculate at least one mean CO 2 content value (Vmean) from the maximum CO 2 content values (Vmax) obtained over the time window (Ft), iv) repeat steps i) to iii) in order to obtain several successive mean CO 2 content values (Vmean) calculated from maximum CO 2 content values (Vmax) obtained over several successive time windows (Ft), and v) transmit the mean CO 2 content values (Vmean) to the graphical user interface, and i) select a maximum CO 2 content value (Vmax) from a plurality of CO 2 content values measured during a given time period (dt) and recorded in the storage means, ii) repeat step i) in order to obtain several successive maximum CO 2 content values (Vmax) measured over a time window (Ft) comprising several successive time periods (dt), iii) calculate at least one mean CO 2 content value (Vmean) from the maximum CO 2 content values (Vmax) obtained over the time window (Ft), iv) repeat steps i) to iii) in order to obtain several successive mean CO 2 content values (Vmean) calculated from maximum CO 2 content values (Vmax) obtained over several successive time windows (Ft), and v) transmit the mean CO 2 content values (Vmean) to the graphical user interface, and B) the graphical user interface is configured to display the mean CO 2 content values (Vmean) in the form of at least one graphical representation.