PROJECT SUMMARY/ABSTRACT Cardiomyopathy is classified into ischemic cardiomyopathy, caused by coronary artery disease, or non- ischemic cardiomyopathy, caused by other factors. The current standard practice for diagnosing the cause of cardiomyopathy is to use coronary angiography to assess the presence or absence of coronary artery disease. However, this approach is flawed and may not always accurately identify the underlying cause of the myocardial disease. Recent advancements in cardiac magnetic resonance imaging allow for a myocardial approach to identifying the cause of cardiomyopathy by directly visualizing myocardial abnormalities, including tissue damage. We hypothesize that a myocardial approach will reclassify the cause of cardiomyopathy in a clinically significant proportion of patients and improve the prediction of long-term outcomes. To test this hypothesis, we will use a large cohort of patients from an institutional registry of consecutive patients undergoing cardiac magnetic resonance imaging for clinical reasons. Our study's anticipated results will provide novel, large-scale data on the cause of cardiomyopathy and its long-term prognostic impact, clarifying the extent of misclassification when using a coronary approach. This information will be essential to conduct a randomized clinical trial comparing a myocardial approach to the coronary approach for identifying the cause of cardiomyopathy. More accurate recognition of the cause of cardiomyopathy will allow for increased use of appropriate cause-specific treatments, improving the long-term outcomes of patients. The study's results will be relevant to the 1 million Americans diagnosed with heart failure and the several thousand others diagnosed with cardiomyopathy without heart failure every year. The proposed work has a high potential to lead to improvements in clinical practice and patient outcomes on a large scale.