This project will develop a new method for the measurement of regional blood perfusion in the heart wall. In this technique, a portion of the heart wall will be heated by a lcm X lcm 2450MHz microwave applicator. After cessation of heating, the decay in myocardial will be measured by either an embedded thermocouple or a surface disk thermistor. The measured temperature decay will be dependent upon regional perfusion, thus allowing perfusion to be calculated from a numerical thermal model of the heart wall. This technique will be more sensitive to the rate of blood perfusion than previously developed thermistor probes. The technique also has advantages over currently employed myocardial perfusion measurement methods in that it provides a quantitative determination of capillary perfusion at low cost and without the use of radioactive substances. A preliminary series of calculations analyzing heat transfer in the heart wall indicates the feasibility of the technique.