PROJECT SUMMARY The health care delivery system is undergoing tremendous changes, with increasing consolidation from mergers and acquisitions, as well as openings and closings of hundreds of emergency departments and hospitals. These changes are typically driven more by the market and financial motivations rather than by identification of need or gaps in access to care. The impact of these changes on access and receipt of high- quality care are largely unknown. These changes may be particularly impactful for acute cardiovascular and cerebrovascular (CV) care. Acute CV events are leading causes of death and disability and patients with acute CV events require timely access to reperfusion interventions for improved outcomes. The geographic distribution of hospitals, and interactions between them through patient transfers, are key to ensuring patients’ receipt of high-quality acute CV care. Mergers and acquisitions of hospitals have potential to improve CV care if they lead to increased investment and improved specialty care at acquired hospitals or to enhanced transfer protocols with improved access to tertiary care. Alternatively, they may lead to harm if they result in reduced access to necessary technology in some communities or inappropriate transfers. The degree of investment versus divestment may vary depending on the characteristics of the acquired hospital and the community it serves. Hospital and emergency department openings and closures may also improve or harm CV care. Closures may reduce access to CV care near where patients live and lead to fatal or disabling delays. Alternatively, closure of lower quality sites may improve outcomes if patients increasingly receive care at higher volume, higher-quality tertiary sites without substantially increasing time to treatment. Openings of new sites may also mitigate the impact of closures if they occur in the same market. However, if openings occur in already well-resourced markets they may widen existing disparities. We aim is to quantify the effects of these market changes on CV patient outcomes, understand the underlying mechanisms, and determine whether they have disproportionate impact on particular patient groups or communities. In Aim 1, we will focus on mergers and acquisitions, and use a quasi-experimental design in national Medicare and Medicaid data to examine their impact on receipt of advanced acute care and outcomes among CV patients, to investigate the mechanisms through which changes occur, and to assess whether there is differential effect by characteristics of the patient or the acquiring site’s parent organizations. In Aim 2, we will use similar methods to examine the impact of openings and closings. Understanding the impact of these two shifts in the health care market on acute CV care and the pathways by which they occur will be key to identifying interventions and strategies to reduce disparities in CV access and outcomes and to inform policy related to regulation of heal...