Method and system for monitoring an internal electrical impedance of a biological object including Internal Thoracic Impedance (ITI) comprising placing two arrays of electrodes on opposite sides of the biological object, wherein each of said two arrays comprise three equally spaced electrodes; imposing an alternating electrical current between pairs of the electrodes and obtaining voltage signals representative of a voltage drop thereon, calculating two values of internal electrical impedance of the biological object corresponding to the uttermost electrodes of said two arrays of electrodes placed on the opposite sides of the biological object.