a pacing system and method for providing multiple chamber pacing of a patient &# 39 ; s heart , and in particular , pacing programmed for treatment of various forms of heart failure . the system utilizes impedance sensing for determining optimum pacing parameters , e . g ., for pacing the left ventricle so that left heart output is maximized . the impedance sensing also is used for determination of arrhythmias or progression of heart failure . impedance sensing is provided for between selected pairs of the four chambers , to enable optimizing of information for control and diagnosis . in a preferred embodiment / of the invention , impedance measurements are obtained for determining the timing of right heart valve closure or right ventricular contractions , and the timing of delivery of left ventricular pace pulses is adjusted so as to optimally synchronize left ventricular pacing with the right ventricular contractions . impedance sensing in the left heart also provides timing of mechanical contraction , and the pacemaker controls pacing to maintain bi - ventricular mechanical synchronization adjusted for maximum cardiac output .