IMPORTANCE Fine particulate matter (smaller than 2.5 μm) (PM 2.5) air pollution is a major global risk factor for cardiovascular (CV) morbidity and mortality. Few studies have tested the benefits of portable air filtration systems in urban settings in the United States. OBJECTIVE To investigate the effectiveness of air filtration at reducing personal exposures to PM 2.5 and mitigating related CV health effects among older adults in a typical US urban location. DESIGN, SETTING, AND PARTICIPANTS This randomized, double-blind crossover intervention study was conducted from October 21, 2014, through November 4, 2016, in a low-income senior residential building in Detroit, Michigan. Forty nonsmoking older adults were enrolled, with daily CV health outcome and PM 2.5 exposure measurements. INTERVENTIONS Participants were exposed to the following three 3-day scenarios separated by 1-week washout periods: unfiltered air (sham filtration), low-efficiency (LE) high-efficiency particulate arrestance (HEPA)-type filtered air, and high-efficiency (HE) true-HEPA filtered air using filtration systems in their bedroom and living room. MAIN OUTCOMES AND MEASURES The primary outcome was brachial blood pressure (BP). Secondary outcomes included aortic hemodynamics, pulse-wave velocity, and heart rate variability. Exposures to PM 2.5 were measured in the participants' residences and by personal monitoring. RESULTS The 40 participants had a mean (SD) age of 67 (8) years (62% men). Personal PM 2.5 exposures were significantly reduced by air filtration from a mean (SD) of 15.5 (10.9) μg/m 3 with sham filtration to 10.9 (7.4) μg/m 3 with LE fitration and 7.4 (3.3) μg/m 3 with HE filtration. Compared with sham filtration, any filtration for 3 days decreased brachial systolic and diastolic BP by 3.2 mm Hg (95% CI, −6.1 to −0.2 mm Hg) and 1.5 mm Hg (95% CI, −3.3 to 0.2 mm Hg), respectively. A continuous decrease occurred in systolic and diastolic BP during the 3-day period of LE filtration, with a mean of 3.4 mm Hg (95% CI, −6.8 to −0.1 mm Hg) and 2.2 mm Hg (95% CI, −4.2 to −0.3 mm Hg), respectively. For HE filtration, systolic and diastolic BP decreased by 2.9 mm Hg (95% CI, −6.2 to 0.5 mm Hg) and 0.8 mm Hg (95% CI, −2.8 to 1.2 mm Hg), respectively. Most secondary outcomes were not significantly improved. CONCLUSIONS AND RELEVANCE Results of this study showed that short-term use of portable air filtration systems reduced personal PM 2.5 exposures and systolic BP among older adults living in a typical US urban location. The use of these relatively inexpensive systems is potentially cardioprotective against PM 2.5 exposures and warrants further research. TRIAL REGISTRATION ClinicalTrials.gov identifier: NCT03334565