Abstract: This study is aimed to evaluate the impact of air pollution on the in-hospital mortality of ischemic heart disease patients in Tehran as a polluted metropolis. A cross sectional study conducted in Tehran heart center. We compared two separate exposure levels of air pollutants in patients expired in hospital (n = 23) versus patients discharged alive (n = 1219). The first was air pollutants daily mean concentration at the date of admission and the second was air pollutants daily mean concentration at the date of admission and the three following days. Patients' demographic, clinical and paraclinical data were gathered from the hospital databank between 23 September and 21 December 2005. Meteorological data were obtained from Tehran air quality control company. In-hospital mortality rate was 1.9% for men and 1.8% for women. The expired patients were older than survived patients. The mean concentration of carbon monoxide, dust, nitrous oxide, other nitrogen compounds and sulfur dioxide were significantly higher and mean temperature was significantly lower at admission date of expired patients. In expired patients, mean concentrations of nitrous oxide, nitrogen dioxide, other nitrogen compounds, sulfur dioxide, dust and non-methane hydrocarbons were significantly higher at admission date and three following days compared to survived patients. There was significant direct relationship between air pollution level and in-hospital mortality of ischemic heart disease patients.