It is verified that rheological factors play a role in the pathomechanism of ischemic heart disease (IHD) and acute myocardial infarction (AMI). The changes of the rheological parameters (whole blood and plasma viscosity, fibrinogen level, hematocrit) of 17 patients (mean age: 59 years) were studied in the first six months after AMI. The measurements were carried out after the admission, before the discharge from the hospital and at the control examinations after one and six months. A slight increase of hematocrit and whole blood viscosity was found during the six months follow up period which was statistically significant concerning the hematocrit (p less than 0.05). As the part of the control examination exercise stress test was performed. Among the rheological parameters hematocrit and whole blood viscosity of those who showed myocardial ischemia during the test were significantly worse (p less than 0.05) comparing to the non ischemic group. These results underline the role of hemorheological parameters as risk factors in these diseases.