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.