An apparatus configured to distinguish near-field atrial activity from far-field ventricular activity, comprising: a processor connectable to an electrocardiographic sensor of ventricular activity and to a cardiac catheter , the catheter having at least one sensing electrode disposed on a distal portion thereof; a display linked to the processor; a memory accessible to the processor storing programs and data objects therein, the programs including a graphical interface program, wherein execution of the programs cause the processor to perform the steps of: when the at least one sensing electrode is in galvanic contact with respective locations in an atrium of a heart acquiring electrograms from the at least one sensing electrode and concurrently detecting ventricular depolarization events in the heart via the electrocardiographic sensor; generating from the electrograms a 4-dimensional local activation time map showing electrical propagation in the heart; and invoking the graphical interface program to present the 4-dimensional local activation time map on the display as a series of visual images, the images including an icon that visually indicates whether a ventricular depolarization event has occurred, wherein the icon is presented using visual indicia which are referenced to detections of ventricular depolarization, and wherein the visual indicia include the same time-window and colour scale as the 4-dimensional local activation time map. a processor connectable to an electrocardiographic sensor of ventricular activity and to a cardiac catheter , the catheter having at least one sensing electrode disposed on a distal portion thereof; a display linked to the processor; a memory accessible to the processor storing programs and data objects therein, the programs including a graphical interface program, wherein execution of the programs cause the processor to perform the steps of: when the at least one sensing electrode is in galvanic contact with respective locations in an atrium of a heart acquiring electrograms from the at least one sensing electrode and concurrently detecting ventricular depolarization events in the heart via the electrocardiographic sensor; generating from the electrograms a 4-dimensional local activation time map showing electrical propagation in the heart; and invoking the graphical interface program to present the 4-dimensional local activation time map on the display as a series of visual images, the images including an icon that visually indicates whether a ventricular depolarization event has occurred, wherein the icon is presented using visual indicia which are referenced to detections of ventricular depolarization, and wherein the visual indicia include the same time-window and colour scale as the 4-dimensional local activation time map. when the at least one sensing electrode is in galvanic contact with respective locations in an atrium of a heart acquiring electrograms from the at least one sensing electrode and concurrently detecting ventricular depolarization events in the heart via the electrocardiographic sensor; generating from the electrograms a 4-dimensional local activation time map showing electrical propagation in the heart; and invoking the graphical interface program to present the 4-dimensional local activation time map on the display as a series of visual images, the images including an icon that visually indicates whether a ventricular depolarization event has occurred, wherein the icon is presented using visual indicia which are referenced to detections of ventricular depolarization, and wherein the visual indicia include the same time-window and colour scale as the 4-dimensional local activation time map. <EOS>