Heart disease is the leading cause of morbidity and mortality in the Western World. As this is mostly related to disorders of the blood supply to the heart, it is very important to be able to assess the perfusion of the heart wall. Conventional methods for assessing myocardial perfusion have many limitations, including relatively low resolution and poor ability to provide quantitative data. Magnetic resonance imaging (MRI) of the "first-pass" kinetics of contrast enhancement by a bolus injection of contrast agent is a very promising method for noninvasive assessment of myocardial perfusion, with higher resolution than conventional radionuclide imaging methods. However, current approaches to MRI perfusion studies have only been "semiquantitative", due to several technical difficulties. We have been achieving very encouraging initial results in making absolute measurements of regional myocardial perfusion, using novel MRI methods that we have designed to overcome the limitations of conventional MRI approaches. In the proposed research, we will further develop our MRI methods, and the associated image analysis methods, for quantitatively measuring myocardial perfusion. We will perform a series of studies on normal subjects to establish the expected range of variability of the results. We will also perform a series of studies of patients with coronary artery disease, comparing the results of our MRI methods with those of conventional methods used to assess the blood supply to the heart, including radionuclide imaging, CT angiography and conventional cardiac catheterization (including invasive measures of flow reserve). The significance of the proposed work is its potential to achieve more accurate and higher resolution assessments of blood flow to the heart wall than current conventional methods can provide. This would be very useful for aiding treatment decisions and for following the results of therapy in patients with ischemic heart disease, a common and serious clinical condition. The quantitative MRI methods we propose to develop for the assessment of cardiac vascular disease may also be applicable to assessment of the perfusion of other important organs, such as the brain, which is subject to stroke, and in other important disease processes, such as cancer, where the disease evolution may be related to blood flow.