Despite the efficacy of many therapies for heart failure, it remains a leading cause of morbidity and mortality worldwide, with many patients progressing to advanced stages of the condition. Since the standard treatment for heart failure includes small-molecule drugs targeting G protein-coupled receptors (GPCRs), GPCRs are still considered novel targets for the diagnosis and treatment of cardiovascular diseases. Corticotropin-releasing hormone receptor 2, a highly expressed GPCR in cardiomyocytes, and its ligand, urocortin2 (UCN2), have been reportedly associated with cardiovascular diseases; however, their clinical significance remains unclear. In this study, a UCN2 measurement assay was developed to measure blood UCN2 levels in patients with heart failure. The assay showed that blood UCN2 values indicated a negative relationship with cardiac ejection fraction in 52 patients with heart failure. Blood UCN2 levels were not correlated with brain natriuretic peptide, a standard marker of heart failure, and were higher in patients with cardiomyopathy than in those with heart failure, suggesting that measuring blood UCN2 levels may be a novel test for assessing the pathophysiology of heart failure.