Hemodynamic and hemogasanalytic comparative study was performed in 46 patients admitted to our Coronary Care Unit because of myocardial infarction. The values of pH; PO2; PCO2; HbaO2; HbvO2; SBP; CVP; PAP; WP; Q; and CI were recorded simultaneously in every patient one or more times during the first 72 hours of the disease. The patients were divided into four classes according to the severity of hemodynamic impairment. Statistical analysis of the obtained results was then performed. In all patients more or less severe hypoxemia was found, but it was not statistically related to the severity of hemodynamic impairment. Instead, the values of PvO2 and HbvO2 showed a very significant correlation with Q and CI. Moreover, in 11 patients the venous admixture (QVA/Q) was measured several times in order to study the cause of the arterial hypoxemia thoroughly. It showed a very significant direct correlation with Q and CI. The interpretation of this phenomenon is then discussed and it is suggested that, in such patients, an increase of cardiac output causes an increased flow through poorly ventilated areas.