epicardium they may be located in the left ventricle or in a coronary vein on the middle of the left ventricle in addition leads comprising a sensor may be located in any suitable position in the body of a patient e g vena cava or other places in thorax with reference now to fig2 the configuration including the primary components of an embodiment of the present invention will be described the illustrated embodiment comprises an implantable medical device 20 such as the pacemaker shown in fig1 leads 26 a and 26 b of the same type as the leads 6 a and 6 b shown in fig1 are connectable to the device 20 the leads 26 a 26 b may be unipolar or bipolar and may include any of the passive or active fixation means known in the art for fixation of the lead to the cardiac tissue as an example the lead distal tip not shown may include a tined tip or a fixation helix the leads 26 a 26 b carry one or more electrodes as described with reference to fig1 such as a tip electrode or a ring electrode arranged to inter alia measure the impedance or transmit pacing pulses for causing depolarization of cardiac tissue adjacent to the electrode s generated by a pace pulse generator 25 under influence of a controller 27 including a microprocessor the controller 27 controls inter alia pace pulse parameters such as output voltage and.