Background: Exposure to particulate matter with an aerodynamic diameter less than or equal to 2.5 μm (PM_2.5) is associated with increased risk of heart disease, but less is known about the relationship at low concentrations. This study aimed to determine the dose-response relationship between long-term PM_2.5 exposure and risk of incident ischemic heart disease (IHD), incident heart failure (HF), and incident atrial fibrillation (AF) in older men living in a region with relatively low ambient air pollution. Methods: PM_2.5 exposure was estimated for 11,249 older adult males who resided in Perth, Western Australia and were recruited from 1996 to 1999. Participants were followed until 2018 for the HF and AF outcomes, and until 2017 for IHD. Cox-proportional hazards models, using age as the analysis time, and adjusting for demographic and lifestyle factors were used. PM_2.5 was entered as a restricted cubic spline to model nonlinearity. Results: We observed a mean PM_2.5 concentration of 4.95 μg/m³ (SD 1.68 μg/m³) in the first year of recruitment. After excluding participants with preexisting disease and adjusting for demographic and lifestyle factors, PM_2.5 exposure was associated with a trend toward increased incidence of IHD, HF, and AF, but none were statistically significant. At a PM_2.5 concentration of 7 μg/m³ the hazard ratio for incident IHD was 1.04 (95% confidence interval [CI] = 0.86, 1.25) compared with the reference category of 1 μg/m³. Conclusions: We did not observe a significant association between long-term exposure to low-concentration PM_2.5 air pollution and IHD, HF, or AF.