The response of the myocardium to burn shock in young and old animals will be assessed from a performance and biochemical perspective. Other forms of shock have indicated that the myocardium undergoes a depression in contractile function during the intermediate-late shock phase and that subcellular alterations may occur in concert with changes in performance. In order to assess myocardial contractile performance in the absence of confusing hemodynamic loading conditions and neurohumoral influences, the isolated perfused isovolumic heart preparation will be used to measure HR, peak LVP, +dP/dt, time to peak +dP/dt, -dP/dt, time to peak -dP/dt, and time to 90% relaxation. Sarcoplasmic reticulum (SR) and mitochondrial function will be examined in this study to determine whether these organelles are compromised following burn shock and to ascertain whether the aged heart has a different biochemical response than the young adult heart. The results of this study will provide a mechanistic basis for evaluating potential therapeutic pharmacological interventions that may prove to be helpful to aged burn patients following thermal injury.