External cardiac compression is now the accepted method of treating sudden cardiac arrest. The technique is described, with particular emphasis on the steps which can cause serious trauma, if not properly performed. Ventilation of the lungs is of paramount importance. The incidence of cardiac arrest seems to be increasing and appears to be higher in infants, perhaps because of the large proportion of cardiac surgical procedures in this age group. Survivals depend on several factors, the most important of which are the time elapsed before treatment is begun, the location of the patient at the time of cardiac arrest, and the primary disease of the patient. Use of external cardiac compression diminishes delay, makes the location of the patient less important, and produces less trauma in a critically ill patient. Blood pressures achieved by the external method are comparable to levels reached by direct massage of the heart. The myocardium is not traumatized by the external method, which is also less fatiguing to the operator. The complications of external cardiac compression are traceable to excessive pressures and to pressure over wrong areas of the chest, and are therefore avoidable. Pressure should be applied to the sternum in the mid-line only, just above the xyphoid process. Two cases of ruptured liver in children are mentioned, and reports of other injuries are discussed in connection with specific errors in technique.