We evaluated, during an exercise test, the leukocyte flow properties, the polymorphonuclear leukocyte (PMN) membrane fluidity and PMN cytosolic Ca
$^{2+}$
content in normals, in subjects with previous acute myocardial infarction (AMI) and in subjects previously submitted to a aortocoronary by‐pass. Leukocyte flow properties were evaluated using the St.George filtrometer. Examination of the PMN membrane fluidity was effected employing the probe TMA‐DPH; while evaluation of the PMN cytosolic Ca
$^{2+}$
content was carried out using the probe Fura 2‐AM. At baseline, in both cardiopathic groups a significant difference in PMN filtration parameters and in PMN cytosolic Ca
$^{2+}$
content was evident compared to normals. In normals, at peak of exercise, there was an evident reduction of mononuclear filtration parameters, while during recovery a slight increase of the PMN cytosolic Ca
$^{2+}$
content was observed. In subjects with previous AMI and in subjects with aortocoronary by‐pass, however, we observed, at peak of exercise, a decrease of the mononuclear filtration parameters, a reduction of the PMN membrane fluidity and an increase of the PMN cytosolic Ca
$^{2+}$
content. In both groups, the changes in PMN membrane fluidity and cytosolic Ca
$^{2+}$
content remained during recovery. The trend of the PMN membrane fluidity and cytosolic Ca
$^{2+}$
content found in the cardiopathic subjects during the exercise test suggest that PMN activation may be more evident in these subjects.
