A late reduction (i.e. 1 hour post exercise) in left ventricular ejection fraction (LVEF) in patients with ischaemic heart disease was recently reported with radionuclide myocardial perfusion imaging (MPI). This was ascribed to possible stunning provoked by exercise-induced ischaemia. The purpose of this retrospective study was to evaluate the possible relationship between exercise-induced ischaemia and late (1 hour) post-exercise myocardial stunning. Forty-eight patients who underwent standard treadmill exercise with 99m Tc-MIBI MPI were analysed according to their rest and stress perfusion images. A normal group of 15 subjects, 23 patients with previous infarction and 10 with objective evidence of ischaemia were identified. Absolute change, i.e. exercise LVEF minus rest LVEF, and relative change, i.e. absolute change divided by resting LVEF (expressed as a percentage) were determined. The mean absolute change in LVEF was not significant within the normal and infarction groups but was statistically significant within the ischaemic group. The mean relative ( %) change within the normal and infarction groups was not significant, but was significant within the ischaemic group. The difference in mean absolute changes between the normal and infarction group was not significant but both these groups were statistically different when compared with the ischaemic group. No statistically significant difference in mean relative changes was found between the normal and infarction groups. The mean relative change in the ischaemic group tended to be larger than in the infarction group. The presence of a late regional wall motion abnormality or decreased LVEF after exercise (i.e. stunning) may be an important additional indicator of underlying myocardial ischaemia.