capacitor c1 is clamped to ground determined by the differentiator circuit 33 and the value of the clamping resistor 17 are related to the various parameters such as the electrode material which determines electrode capacitance and the value of the output coupling capacitor so as to achieve this discharge in the required time it is considered an advantage of the invention that proper compensation can be achieved by this method for a wide range of stimulation current levels as indicated on line l6 after the clamp is removed and during the time period for verifying capture 18 milliseconds to 110 milliseconds as indicated by the dashed portion there is a residual charge resulting in voltage level 42 but the rate of change of voltage is very small compared to the rate of change of voltage that would otherwise occur if there were no clamping the slight offset voltage 42 is a function of system parameters and it is accounted for when the amplifier is reconnected the output of the iwen generator 27 is also fed to a second differentiator circuit 28 the output of which is connected to the gate of switch d the time constant of the differentiator circuit 28 is longer than the longest time constant for the differentiator 33 but less than the duration of the iwen signal so that the signal input 18 of the amplifier 20 may be disconnected during stimulation and clamping but reconnected to the heart electrode prior to removal of amplifier restraint to be discussed presently this is illustrated.