This double-blind, randomized, crossover trial aims to test the hypothesis that longer-term indoor air filtration intervention can slow atherothrombosis progression by reducing indoor fine particulate matter (PM2.5) exposure in adults with ischemic heart disease history.

This double-blind, randomized, crossover trial will recruit 112 adults with ischemic heart disease history and will investigate potential benefits of indoor high efficiency particulate air (HEPA) filtration on ameliorating the progression of atherothrombosis. Participants will be contacted and recruited to the study based on inclusion and exclusion criteria. After consenting, participants will go through a total of 21-month study period comprised of true HEPA filtration and sham filtration, each of 9-month in duration, and a 3-month wash-out period. After 3-month wash-out period, participants will be switched to the other arm of the intervention. During the trial, project specialists will complete a series of home visits before, in the middle, and after each intervention session to set up air purifiers and indoor and outdoor air pollution monitors, as well as conduct interview to collect questionnaire data, measure vascular function, blood pressure, and collect biospecimens. Participants will self-monitor their daily blood pressure through out the intervention periods. In aim 1, researchers will assess the effect of a 9-month residential HEPA intervention on atherothrombosis progression in 112 participants. In aim 2, the researchers will examine the association between reduction in indoor PM2.5 exposure brought by the intervention and the changes in atherothrombosis progression indicators adjusting for outdoor PM2.5 exposure. In aim 3, researchers will examine atherothrombosis responses (both levels and slopes of change) to the HEPA intervention within four subgroups of participants: 1) non-Hispanics, 2) Hispanics, 3) females, and 4) males.

Inclusion Criteria:

• Age between 65 and 84 years old;
• Weight ≥ 110 pounds;
• Nonsmokers for at least 1 year;
• Have ischemic heart disease history, clinically stable for 6 months, without any deterioration in symptoms or episodes of angina based on past electronic medical records;
• Both English and Spanish speaking participants will be included in the recruitment;
• Live in the Los Angeles County.

Exclusion Criteria:

• Have history of degenerative disease of the nervous system such as dementia and Alzheimer's;
• Currently have active cancer treatments;
• The residential house has already had HEPA filters;
• Participants will move out from the current residential address in the next 2 years;
• Participants will spend more than 1 month living outside the primary home;
• Have any health conditions that prohibit collecting health and covariate data and biospecimens;
• Participants' residential houses are not feasible for setting up air purifiers and air pollutants monitors.

A sham filter will be used in the control, to replace HEPA filter in the intervention group. Participants and investigators will be blinded to the intervention type, only investigators who will prepare air filters for intervention will be unblinded for the real air filter type.