Abstract: Provided herein are methods for diagnosing cardiomyopathy by evaluating a sample from a subject for the presence of a population of activated fibroblasts comprising a particular genetic signature (e.g., a genetic signature comprised of differential expression of one or more gene products relative to a normal subject or a population of normal subjects). The one or more gene products may include POSTN, COL22A1, and/or THBS4. Also provided herein are methods for treating cardiomyopathy and for modulating the activity of one or more gene products associated with activation of cardiac fibroblasts in a subject using an agent. Compositions comprising an agent for treating cardiomyopathy and kits for diagnosing cardiomyopathy are also provided by the present disclosure.