A Leadless Cardiac Pacemaker LCP comprising: an outer housing ; a plurality of exposed electrodes connected relative to the outer housing; and a controller disposed within the outer housing and operatively connected to the plurality of exposed electrodes, wherein the controller is configured to: deliver pacing pulses to the plurality of exposed electrodes at a base pacing rate ; detect a measure of metabolic demand , wherein the measure metabolic demand varies over time; deliver pacing pulses at an elevated pacing rate relative to the base pacing rate after determining that the measure of metabolic demand is elevated with respect to a base measure of metabolic demand, wherein the elevated pacing rate varies with time and is dependent on the detected measure of metabolic demand; change a heart stress tracking value during times when pacing pulses are delivered at the elevated pacing rate, wherein the heart stress tracking value is changed faster during times when higher elevated pacing rates are delivered relative to times when lower elevated pacing rates are delivered; and determine if the heart stress tracking value crosses a predetermined heart stress threshold, and if so, reduce the elevated pacing rate back toward the base pacing rate. an outer housing ; a plurality of exposed electrodes connected relative to the outer housing; and a controller disposed within the outer housing and operatively connected to the plurality of exposed electrodes, wherein the controller is configured to: deliver pacing pulses to the plurality of exposed electrodes at a base pacing rate ; detect a measure of metabolic demand , wherein the measure metabolic demand varies over time; deliver pacing pulses at an elevated pacing rate relative to the base pacing rate after determining that the measure of metabolic demand is elevated with respect to a base measure of metabolic demand, wherein the elevated pacing rate varies with time and is dependent on the detected measure of metabolic demand; change a heart stress tracking value during times when pacing pulses are delivered at the elevated pacing rate, wherein the heart stress tracking value is changed faster during times when higher elevated pacing rates are delivered relative to times when lower elevated pacing rates are delivered; and determine if the heart stress tracking value crosses a predetermined heart stress threshold, and if so, reduce the elevated pacing rate back toward the base pacing rate. deliver pacing pulses to the plurality of exposed electrodes at a base pacing rate ; detect a measure of metabolic demand , wherein the measure metabolic demand varies over time; deliver pacing pulses at an elevated pacing rate relative to the base pacing rate after determining that the measure of metabolic demand is elevated with respect to a base measure of metabolic demand, wherein the elevated pacing rate varies with time and is dependent on the detected measure of metabolic demand; change a heart stress tracking value during times when pacing pulses are delivered at the elevated pacing rate, wherein the heart stress tracking value is changed faster during times when higher elevated pacing rates are delivered relative to times when lower elevated pacing rates are delivered; and determine if the heart stress tracking value crosses a predetermined heart stress threshold, and if so, reduce the elevated pacing rate back toward the base pacing rate. <EOS>