Accurate nontraumatic measurement of cardiac output is necessary to aid in diagnosing cardiovascular disorders, noting progress during intensive care, assessing effectiveness of palliative measures, and broadening the quality of cardiovascular research. Due to variability in results obtained by clinical thermo-dilution and dye dilution methods, at best only an estimate of cardiac output is obtained. The proposed research deals with the development of a new method for the nonsurgical measurement of cardiac output for use in experimental animals and humans. An ultrasonic esophageal probe placed in the region of the heart can be used to ultrasonically illuminate and hence measure the flow in the pulmonary artery, descending aorta and the major arteries to the head. Cardiac output is equivalent to main pulmonary artery flow or descending aorta flow plus flow in arteries to the head. Prototype ultrasonic probes have been built and the feasibility of measuring aortic flow has been demonstrated both in dogs and man. Additional ultransonic esophageal probes will be designed to be used in conjunction with our pulsed ultrasound Doppler velocity meter and echo track. Initial efforts will be directed toward in vivo mapping the hemodynamics in vessels emanating from the heart ad determining the most accurate means for measuring flow in these vessels. Following careful evaluation of the esophageal probe technique we will compare esophageal probe values for cardiac output with those obtained by dye dilution or thermo-dilution in mongrel dogs. A minicomputer will be interfaced with the instrumentation to provide rapid printout of cardiac output. The results will be 1) the development of a new technique for the measurement of cardiac output and 2) a detailed comparison among clinical methods used to measure cardiac output. The new method should improve the ease and accuracy of the clinical determination of blood flow from the heart. Ultrasonic catheters will also be developed for a more invasive, yet accurate measure of flow in the aorta or pulmonary artery.