Measurement of regional myocardiac blood flow using Positron Emission Tomography. Three PET blood flow methodologies will be investigated -0-15 labeled water bolus injection, N-13 labeled ammonia, and Rubidium 82. Methods for compensating for partial volume effects and """"""""spill over"""""""" from the LV cavity will be developed. The resultant flow values will be compared to microsphere measurements in 10 dogs.