Several imaging techniques have been used to assess cardiac structure and function, to understand pathophysiology, and to guide clinical decision making in the setting of acute coronary syndromes (ACS). Over the last years, cardiac positron emission tomography (PET) has affirmed its role in this setting. Indeed, the combined quantitative assessment of myocardial metabolism and perfusion has allowed to better understand the functional status of infarcted and non-infarcted myocardium, thus improving our knowledge of myocardial response to necrosis. More recently, several studies, taking advantage of previous observations in patients with cancer, have shown that PET could also provide important information on the mechanisms of vascular instability through the early identification of activated inflammatory cells in the atherosclerotic plaque. These findings are opening the way to more effective forms of prevention of acute vascular syndromes in high-risk patients; furthermore, new more sensitive and specific tracers for the identification of vascular inflammation are under development. In this review, we describe the potential and limitations of PET in the assessment of ACS.