Abstract-Air pollution is a heterogeneous, complex mixture of gases, liquids, and particulate matter. Epidemiological studies have demonstrated a consistent increased risk for cardiovascular events in relation to both short-and long-term exposure to present-day concentrations of ambient particulate matter. Several plausible mechanistic pathways have been described, including enhanced coagulation/thrombosis, a propensity for arrhythmias, acute arterial vasoconstriction, systemic inflammatory responses, and the chronic promotion of atherosclerosis. The purpose of this statement is to provide healthcare professionals and regulatory agencies with a comprehensive review of the literature on air pollution and cardiovascular disease. In addition, the implications of these findings in relation to public health and regulatory policies are addressed. Practical recommendations for healthcare providers and their patients are outlined. In the final section, suggestions for future research are made to address a number of remaining scientific questions. Key Words: AHA Scientific Statements Ⅲ air pollution Ⅲ cardiovascular diseases Ⅲ respiration R ecently, the American Heart Association (AHA) published "Guidelines for Primary Prevention of Cardiovascular Disease and Stroke" as an aid to healthcare professionals and their patients without established coronary artery disease or other atherosclerotic diseases. 1 The statement was intended to complement the AHA/American College of Cardiology (ACC) "Guidelines for Preventing Heart Attack and Death in Patients with Atherosclerotic Cardiovascular Disease." 2 Both sets of recommendations emphasized multifactorial interventions, especially more intensive measures/ goals to modify individual cardiovascular risk factors with diet, drugs, exercise, weight management, complete smoking cessation, and avoidance of secondhand smoke (SHS), or combinations thereof.Over the last decade, however, a growing body of epidemiological and clinical evidence has led to a heightened concern about the potential deleterious effects of ambient air pollution on health and its relation to heart disease and stroke. Of special interest are several environmental air pollutants that include carbon monoxide, oxides of nitrogen, sulfur dioxide, ozone, lead, and particulate matter ("thoracic particles" [PM 10 ] Ͻ10 m in aerodynamic diameter, "fine particles" [PM 2.5 ] Ͻ2.5 m, and "coarse particles" [PM 10 to 2.5 ]). These pollutants are associated with increased hospitalization 3 and mortality due to cardiovascular disease, 4 -6 especially in persons with congestive heart failure, frequent arrhythmias, or both. 7 The well-established causal associations between active and passive smoking with heart disease and stroke support the plausibility of an adverse effect of PM on the cardiovascular system.The most recent analysis of the National Mortality and Morbidity Air Pollution Study (NMMAPS), based on data from 90 of the largest cities in the United States, estimated that daily total and cardiopulmonary mortality incr...