A catheterization system , comprising: an irrigation pump ; a flexible catheter adapted for insertion into a heart of a living subject, having a distal portion and a lumen for passing an electrically conductive fluid therethrough to exit the catheter at the distal portion, the lumen connectable to the irrigation pump to form a fluid communication therewith, the catheter having a catheter handle ; a fluid reservoir directly connected to an inflow of the irrigation pump , by a first hydraulic line , such that the reservoir , the pump and catheter handle are connected in series, for supplying the electrically conductive fluid to the catheter; a connector connected to an outflow of the irrigation pump by a hydraulic line and connected to the catheter handle , the connector comprising: an outer metal shell ; a lumen filled with an electrically conductive net or sponge and configured to allow the flow through the lumen of the electrolyte containing fluid; and an electrical connector on the metal shell; electrocardiogram circuitry connectable to the subject for monitoring electrical activity in the heart, the electrocardiogram circuitry including a patient interface unit having an analog input and an isolated ground; and an electrically conductive cable connected between the electrical connector and a body surface electrode that is attachable to the subject; wherein the electrical connector on the metal shell provides electrical continuity between electrolyte containing fluid flowing through the lumen of the connector , the electrically conductive net or sponge and the electrically conductive cable . an irrigation pump ; a flexible catheter adapted for insertion into a heart of a living subject, having a distal portion and a lumen for passing an electrically conductive fluid therethrough to exit the catheter at the distal portion, the lumen connectable to the irrigation pump to form a fluid communication therewith, the catheter having a catheter handle ; a fluid reservoir directly connected to an inflow of the irrigation pump , by a first hydraulic line , such that the reservoir , the pump and catheter handle are connected in series, for supplying the electrically conductive fluid to the catheter; a connector connected to an outflow of the irrigation pump by a hydraulic line and connected to the catheter handle , the connector comprising: an outer metal shell ; a lumen filled with an electrically conductive net or sponge and configured to allow the flow through the lumen of the electrolyte containing fluid; and an electrical connector on the metal shell; an outer metal shell ; a lumen filled with an electrically conductive net or sponge and configured to allow the flow through the lumen of the electrolyte containing fluid; and an electrical connector on the metal shell; electrocardiogram circuitry connectable to the subject for monitoring electrical activity in the heart, the electrocardiogram circuitry including a patient interface unit having an analog input and an isolated ground; and an electrically conductive cable connected between the electrical connector and a body surface electrode that is attachable to the subject; wherein the electrical connector on the metal shell provides electrical continuity between electrolyte containing fluid flowing through the lumen of the connector , the electrically conductive net or sponge and the electrically conductive cable . <EOS>