In this paper, I examine the impact of uninsured patients on the health of the insured, focusing on one health outcome – the in-hospital mortality rate of insured heart attack patients. I employ panel data models using patient discharge and hospital financial data from California (1999{2006). My results indicate that uninsured patients have an economically signi cant e ect that increases the mortality rate of insured heart attack patients. I show that these results are not driven by alternative explanations, including reverse causality, patient composition effects, sample selection or unobservedtrends and that they are robust to a host of speci cation checks. My results also indicate that the primary channel for the observed spillover effects is increased hospital uncompensated care costs. Although data limitations constrain my capacity to check how hospitals change their provision of care to insured heart attack patients in response to reduced revenues, the evidence I have suggests a modest increase in the quantity of cardiac services without a corresponding increase in hospital staff.
