BACKGROUND It is thought that biological responses to air pollutants affect various heart diseases, with the magnitude of the effect dependent on the specific disease. The short-term effects of fine particulate matter (PM(2.5)) on mortality for heart diseases were examined in 9 Japanese cities from 2002 to 2004. RESULTS Mortality data obtained from the Ministry of Health, Labour and Welfare of Japan and PM(2.5) data from the National Institute for Environmental Studies were used in a generalized linear model to evaluate the association between PM(2.5) concentration and the mortality, adjusted for ambient temperature, relative humidity, seasonality, and day of the week. The area-specific results were combined using meta-analysis with a random-effects model. Of 67,897 deaths from heart disease, a significantly positive association was observed between heart disease mortality and PM(2.5) at lag 0. In the age-stratified analyses, the effect of PM (2.5) on acute myocardial infarction, and cardiac arrhythmia and conduction disorders was stronger at lag 0 for the younger population (0-64 years). The associations were not clear in mortality of the elderly. CONCLUSIONS Positive associations between PM (2.5) and heart disease mortality in Japan were observed. The effects of PM(2.5) may vary by disease and age.