The assessment of myocardial function in vivo following trauma and hemorrhage is implicated as one of the most critical approaches to deciphering physiological mechanism and designing a therapeutic strategy. The precise and accurate determination of the physiological function in preclinical animal models will provide important evidence for developing an effectively therapy and unravelling the deep mechanism(s) attributable for pathological disorders and therapeutic intervention. In vivo non-invasive approaches have served as a powerful technology to elucidate these physiological functions. We and others have extensively used in vitro and invasive methods to determine cardiac functioning in small animal studies, providing crucial analysis of cardiac performance in experimental design. However, those approaches and methodological tools with in vitro and invasive techniques were designed to be performed at the end stage of the study and at the expense of euthanizing animals in the studies, which limits obtaining the in vivo assessment of cardiac performance in a serial manner to monitor the progress of experimental studies. The deficiencies include the limitation of measurements and the lack of real time monitoring. In this parent R01 grant, we will determine cardiac function of mice that are subjected to hemorrhage and resuscitation, in vivo measurement of cardiac function by echocardiographic assessment will be conducted in real time and in a non-invasive manner. We have employed echocardiographic analysis of myocardial performance in mouse using the conventional ultrasound for acquisition of data, however, false negative and positive signals, high background noise of imaging measurement frequently occur due to the limitation of the low frequency of transducer. In order to ensure the rigorousness and solidity of our study, we will request to include the most advanced technology by implementing a high- resolution micro-ultrasound the Vevo® 3100 LT imaging system that is specifically designed for small animals to determine in vivo cardiac function. The advantages with employment of the high resolution ultrasound technology the Vevo® 3100 LT imaging systemin our research not only provide a comprehensive array of accurate and serial analyses of cardiovascular function for the proposed studies, but it will also impact our long- standing focus on studying physiological function in small animals by strengthening our ongoing support, improving the knowledge of trainees, and benefiting the greater research community and NIH-funded research.