An implantable medical device for monitoring ventricular synchrony of a heart including a pace pulse generator adapted to produce cardiac stimulating pacing pulses and being connectable to at least one medical lead (20,30) for delivering stimulation pulses to cardiac tissue of said heart, comprising: an impedance measuring unit adapted to, during impedance measuring sessions, measure impedance signals obtained by an electrode configuration being located such that said impedance signals substantially reflects septal wall movements, wherein the electrodes of said electrode configuration are connectable to said implantable medical device; an impedance peak detecting unit adapted to process said impedance signals to determine an impedance signal morphology and to detect impedance amplitude peaks in said impedance signal morphology; and characterized by: a synchronicity index determining unit adapted to: determine a first synchronicity index indicating a degree of synchronicity based on detected impedance peaks within a time window corresponding to systole, wherein at least two impedance peaks indicates an increased dyssynchronicity; determine a second synchronicity index indicating a degree of synchronicity based on detected impedance peaks within a time window corresponding to diastole, wherein at least two impedance peaks indicates an increased dyssynchronicity; associate a weight to said first and second synchronicity index, respectively; and optimize a total synchronicity index based on said first and second synchronicity index to obtain a minimized total index or optimizing said first and second synchronicity index separately to obtain a minimized index in systole and diastole, respectively. an impedance measuring unit adapted to, during impedance measuring sessions, measure impedance signals obtained by an electrode configuration being located such that said impedance signals substantially reflects septal wall movements, wherein the electrodes of said electrode configuration are connectable to said implantable medical device; an impedance peak detecting unit adapted to process said impedance signals to determine an impedance signal morphology and to detect impedance amplitude peaks in said impedance signal morphology; and characterized by: a synchronicity index determining unit adapted to: determine a first synchronicity index indicating a degree of synchronicity based on detected impedance peaks within a time window corresponding to systole, wherein at least two impedance peaks indicates an increased dyssynchronicity; determine a second synchronicity index indicating a degree of synchronicity based on detected impedance peaks within a time window corresponding to diastole, wherein at least two impedance peaks indicates an increased dyssynchronicity; associate a weight to said first and second synchronicity index, respectively; and optimize a total synchronicity index based on said first and second synchronicity index to obtain a minimized total index or optimizing said first and second synchronicity index separately to obtain a minimized index in systole and diastole, respectively. a synchronicity index determining unit adapted to: determine a first synchronicity index indicating a degree of synchronicity based on detected impedance peaks within a time window corresponding to systole, wherein at least two impedance peaks indicates an increased dyssynchronicity; determine a second synchronicity index indicating a degree of synchronicity based on detected impedance peaks within a time window corresponding to diastole, wherein at least two impedance peaks indicates an increased dyssynchronicity; associate a weight to said first and second synchronicity index, respectively; and optimize a total synchronicity index based on said first and second synchronicity index to obtain a minimized total index or optimizing said first and second synchronicity index separately to obtain a minimized index in systole and diastole, respectively. determine a first synchronicity index indicating a degree of synchronicity based on detected impedance peaks within a time window corresponding to systole, wherein at least two impedance peaks indicates an increased dyssynchronicity; determine a second synchronicity index indicating a degree of synchronicity based on detected impedance peaks within a time window corresponding to diastole, wherein at least two impedance peaks indicates an increased dyssynchronicity; associate a weight to said first and second synchronicity index, respectively; and optimize a total synchronicity index based on said first and second synchronicity index to obtain a minimized total index or optimizing said first and second synchronicity index separately to obtain a minimized index in systole and diastole, respectively.