An analysis of electrocardiograms (ECG lead II) obtained following blunt thoracic impacts conducted on 12 anesthetized pigs indicated that all animals developed some degree of trauma to the heart conducting system: sino-atrial nodal disturbances, atrio-ventricular junctional dysfunction, intraventricular conduction defects (e.g., bundle branch blocks), or ventricular fibrillation. The induced ventricular fibrillation proceeded rapidly to the demise of four animals in this study. A comparison of the occurrence of ventricular fibrillation with measured biomechanical response parameters indicated a significant correlation of ventricular dysfunction with high levels of sternal acceleration (930 g) and impact velocity (10.7 m/s). The initiation of ventricular fibrillation did not correlate with typical biomechanical thoracic injury "indicators" (i.i., level of normalized thoracic deflection, cumulative AIS, peak spinal acceleration, or applied force). An injury severity classification (MCD) was subsequently developed for the evaluation of myocardial conducting system dysfunctions.