Background: Epidemiological studies have shown that ambient particulate matter (PM) and changes in air temperature are associated with increased cardiopulmonary events. Objective: We hypothesized that patients with previous myocardial infarction (MI) experience changes in heart rate (HR) and repolarization parameters, such as Bazett-corrected QT interval (QTc), and T-wave amplitude (Tamp), in association with increases in air pollution and temperature changes. Methods: Between May 2003 and February 2004, 67 MI survivors from the Augsburg KORA-MI registry repeatedly sent 16 sec electrocardiograms (ECGs) with a personal transmitter (Viapac) via telephone to the Philips Monitoring Center, where ECG parameters were immediately analyzed. Meteorological data and air pollutants were acquired from fixed monitoring sites on an hourly basis. Additive mixed models were used for analysis. Effect modification by patient characteristics was investigated. Results: The analysis of the 1,745 ECGs revealed an increased HR associated with interquartile range (IQR) increases in PM levels among participants not using beta-adrenergic receptor blockers and among those with body mass index ³ 30 kg/m 2. We observed a 24- to 47-hr lagged QTc prolongation [0.5% change (95% confdence interval, 0.0-1.0%)] in association with IQR increases in levels of PM ² 2.5 _m in aerodynamic diameter, especially in patients with one [0.6% (0.1-1.0%)] or two [1.2% (0.4-2.1%)] minor alleles of the nuclear factor (erythroid-derived 2)-like 2 (NFE2L2) single-nucleotide polymorphism rs2364725. Positive immediate (0-23 hr) and inverse delayed (48-71 hr up to 96-119 hr) associations were evident between PM and Tamp. We detected an inverse U-shaped association between temperature and Tamp, with a maximum Tamp at 5¡C. Conclusions: Increased air pollution levels and temperature changes may lead to changes in HR and repolarization parameters that may be precursors of cardiac problems.