Haematologic abnormalities are found in patients who develop acute ischaemic syndromes including acute myocardial infarction (AMI). A coronary care unit population of 660 consecutive patients were studied for their haematologic parameters on admission. There were 263 patients who had AMI, 207 who had non-infarct acute ischaemic syndromes (CAD), and the other 190 non-coronary patients served as controls. Overall patients with AMI had signijicantly higher haemoglobin (145 ± 2.2 vs 12.9 ± 3.0 g/dl, p<0.0001), haematocrit (45.4 ± 5.8% vs 41.2 ± 8.8%. P < 0.001). red cell count (5.0 ± 0.7 vs 4.5 ± 10^12 p<0.001), but there were no significant differences in their leucocyte count, platelet count or mean corpuscular volume. Patients with CAD had higher haemoglobin and red cell counts (p<0.002, p<0.02 respectively). Although infarct women tended to have lower counts (p<0.001), they still had significantly higher haemoglobin (p<0.01), haematocrit (p<0.02) and red cell count(p<0.002) when compared with controls. Interestingly, there were no ethnic differences at all with regard to haematologic values for infarct patients; haemoglobin, haematocrit, and red count were each significantly higher than controls. Our results suggest that a relatively high baseline Hb, haematocrit or RBC count may be associated with increased likelihood of acute ischaemic syndromes including AMI among Malaysians. Increased viscosity and abnormal haemorheological characteristics may contribute to the development and subsequent outcome of unstable coronary syndromes. Keywords: acute myocardial infarction, coronary artery disease, haemoglobin, haematocrit, haemorheology.