Suppression of tumorigenicity 2 (ST2) is a member of the interleukin (IL)-1 receptor family, whose role was originally established in the context of inflammatory and autoimmune diseases. More recently, testing for ST2 has been used in the setting of cardiovascular disease. The soluble form of ST2 is a decoy receptor that inhibits beneficial cardioprotective effects of IL-33; such inhibition results in cardiac hypertrophy, myocardial fibrosis, and ventricular dysfunction. Measurement of soluble ST2 has utility for assessing heart failure severity and prognosis. In this review, we examine the role of soluble ST2 in both acute and chronic heart failure.