BACKGROUND: Although numerous studies have shown an association between physical activity and coronary heart disease (CHD) mortality in healthy persons, few have reported on this relation in individuals with pre-existing diseases, such as ischaemia. Further, we are unaware of any study to examine if this relationship is modified by the symptomatic nature of the ischaemia. METHODS: To explore these issues, we analysed data from a 25 year follow-up of mortality for 6474 male British civil servants who underwent a resting electrocardiogram and responded to queries regarding angina at study entry. RESULTS: Among men who had ECG abnormalities but no angina (i.e. asymptomatic), activity was associated with a higher rate of CHD mortality. Among men with both angina and ECG abnormalities (i.e. symptomatic), activity was associated with lower CHD mortality but this was not statistically significant at conventional levels. CONCLUSIONS: In the present study, there was a suggestion that the symptomatic nature of ischaemia appeared to modify the effect of physical activity on total and CHD mortality. Although these findings should be examined in other studies, they point to the need for a pre-participation medical examination in active persons or those contemplating embarking on an activity programme.