Cardiovascular disease is the number one cause of death globally and air pollution can be a contributing cause. Acute myocardial infarction and cardiac arrest are frequent manifestations of coronary heart disease. The objectives of the study were to investigate the association between 4 657 out-of-hospital cardiac arrests (OHCA) and hourly and daily outdoor levels of PM10, PM2.5, coarse fraction of PM (PM10-2.5), ultrafine particle proxies, NOx, NO2, O3 and CO in Copenhagen, Denmark, for the period 2000–2010.