There is an ongoing search for biomarkers that can facilitate the diagnosis of subclinical or clinically manifest cardiovascular disease. One of the emerging biomarkers currently under investigation is ST2, which is the receptor of Interleukin-33 (IL-33). ST2 is a member of the Interleukin-1 receptor family and exists in a transmembrane (ST2L) and a soluble form (sST2) due to alternative splicing. Several groups have reported sST2 elevations in serum of cardiovascular disease patients. There is consisting evidence that sST2 is independently predictive for mortality in patients with heart failure or myocardial infarction. In addition to its potential as a biomarker for adverse cardiovascular events, ST2 is considered to play a causal role in chronic cardiovascular diseases such as atherosclerosis and heart failure. Signaling of IL-33 via ST2 has been shown to be cardioprotective in mouse models of myocardial infarction, heart transplantation and cardiac hypertrophy and fibrosis. Furthermore, treatment with IL-33 reduced the development of plaques in atherosclerotic mice. In this paper we will review the currently available literature on sST2 as a biomarker for adverse cardiovascular events. In addition, we will elaborate on the potential mechanistic role of the IL-33/ST2 pathway in chronic inflammatory cardiovascular diseases.