A diagramming system has been developed to assist in interpreting dual chamber pacemaker electrocardiograms. The system is based on the ladder diagram principle but uses two separate ladders, one for the ECG allowing proper representation of atrial A-V and ventricular activation, and a second ladder diagram below it for pacemaker events. The system is applicable to all current single and dual chamber pacing modes and is easy to draw. The ladder diagram allows the logical sequence of timing events to be easily illustrated, and pacemaker malfunction becomes clearly recognizable as a conflict between the ECG events ladder and the pacemaker timing ladder. The system is easy to apply and may eventually prove suitable for automatic generation by computer utilizing sophisticated pacemaker telemetry.