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Background— Daily variations in ambient particulate air pollution have been associated with cardiovascular mortality and morbidity. We therefore assessed the associations between levels of the 3 main modes of urban aerosol distribution and the occurrence of ST-segment depressions during repeated exercise tests.

Methods and Results— Repeated biweekly submaximal exercise tests were performed during 6 months among adult subjects with stable coronary heart disease in Helsinki, Finland. Seventy-two exercise-induced ST-segment depressions >0.1 mV occurred during 342 exercise tests among 45 subjects. Simultaneously, particle mass <2.5 μm (PM2.5) and the number concentrations of ultrafine particles (particle diameter 10 to 100 nm [NC_0.01–0.1]) and accumulation mode particles (100 to 1000 nm [NC_0.1–1]) were monitored at a central site. Levels of particulate air pollution 2 days before the clinic …