A method for monitoring the state of the myocardium during cardiosurgical interventions based on thermal IR imaging is presented. This method called Active Dynamic Thermography (ADT) uses an external excitation source to induce thermal transient processes in a tested object. Recording time series of thermograms allows to calculate parametric images - distribution of the thermal time constant at the visible surface of the myocardium - correlated to the physiology state of tested tissues. In the experiment performed the blood arrest in the left ventricle (causing in longer period heart infarct) was generated by clamping the left anterior descending artery (LAD). During LAD occlusion the ADT procedure was applied using cooling external excitation source. In summary, the calculated time constant images provide data of the tested structure and functional information of myocardium infarct. This allows to track changes in blood flow in the myocardium and inspection of the quality of the intervention during cardiosurgical procedures.