Alterations of the electrocardiogram, blood pressure, and myocardial histological findings were produced in dogs subjected to cervical spinal cord injury. Enhanced sympathetic discharge is the primary event, occurring within seconds of injury, and is manifested by hypertension and tachycardia. Parasympathetic effects occur secondarily and are revealed by a variety of cardiac arrhythmias. Fuchsinophilic degeneration of myocardial cells is seen in spinal cord injured animals. This lesion is similar to that produced by experimental brain stimulation and seen clinically with intracranial hemorrhage. Clinical observations and these studies emphasize the need for early evaluation of the cardiovascular status in acute spinal cord injuries.