Ambulance diversion, which occurs when a hospital emergency department (ED) is temporarily closed to incoming ambulance traffic, is an important system-level interruption that causes delays in treatment and potentially lower quality of care. There is little empirical evidence investigating the mechanisms through which ambulance diversion might affect patient outcomes. We investigated whether ambulance diversion affects access to technology, likelihood of treatment, and ultimately health outcomes for Medicare patients with acute myocardial infarction in twenty-six California counties. We found that patients whose nearest hospital ED had significant ambulance diversions experienced reduced access to hospitals with cardiac technology. This led to a 4.6 percent decreased likelihood of revascularization and a 9.8 percent increase in one-year mortality compared to patients who did not experience diversion. Policy makers may wish to consider creating a policy to specifically manage certain time-sensitive conditions that require technological intervention during periods of ambulance diversion.