Abstract: The methods and assays described herein related to the diagnosis, prognosis and treatment of cardiomyopathy, e.g. arrhythmia. As described herein, the inventors have discovered that certain compounds can be used to treat cardiomyopathies. These compounds are demonstrated herein to reduce expression of nppb, reduce bradycardia, improve contractility, and increase survival. Notably, provided herein is data demonstrating that administration of these compounds can both prevent the development of symptoms when administered prophylactically and reduce symptom severity in subjects where it is administered after the development of symptoms.