Fischer 344 (SPF) rats were exposed by inhalation to respirable paniculate levels of 2 mg/m3diesel emissions, diesel emissions plus coal dust, coal dust, or air for 7 h/d, 5 d/wk for 24 mo. The effects of treatment on body and heart weights, right and left ventricular wall thickness, severity of cardiomyopathy, and changes in the small pulmonary arteries were evaluated after 24 mo of exposure. In all dust‐exposed animals, light microscopic examination of the lungs revealed dust‐laden macrophages in alveolar spaces and focal accumulations of dust‐laden macrophages near the respiratory bronchioles associated with hyperplasia of type II cells. This response was more prominent in animals exposed to diesel emissions alone. Age‐related myocardial fibrosis and inflammatory infiltrates were common in all four groups. No statistically significant differences were detected between the groups for heart weights, ventricular wall thickness, and pulmonary arterial wall thickness. However, animals exposed to diesel emissions did show a consistent trend toward increased pulmonary arterial wall thickness, for all size categories of artery, compared to controls.