In 22 patients with a first myocardial infarction the authors assessed the relationship between morphological changes of the QRS complex and systolic left ventricular function. Using a 56-lead computer-assisted electrocardiogram from the precordium in the form of a map (apparatus Cardiomap-1), the authors prepared a record during the first days after initiating treatment with a thrombolytic agent and again after a period of three weeks. They found only one correlation between the decrement of Q waves and the increase of the left ventricular ejection fraction (p less than 0.05). This correlation, however, is of no practical importance due to the low correlation coefficient. The relationship is moreover markedly influenced by the time of the first record. After the third day of thrombolytic treatment it is not expedient to make the initial record. No relationship between the change of R waves, ST segments and left ventricular function was found. Similarly, due to the great dispersal of values it is not possible to differentiate between patients with inferior infarctions of the heart muscle and anterior myocardial infarctions.