The procedure used to restart the action of the heart if it is suddenly arrested. In many cases the arrested heart can be made to start beating again by rhythmic compression of the chest wall. This is done by placing the patient on a hard surface – a table or the floor – and then placing the heel of the hand over the lower part of the sternum and compressing the chest wall firmly, but not too forcibly to a depth of about 5–6 cms, at the rate of 100–120 times a minute with full release between each compression. Ideally two mouth-to-mouth (or mask) respirations are given after each 30 compressions but untrained bystanders are advised to give chest compressions only so as not to interrupt heart massage. (See APPENDIX 1: BASIC FIRST AID.) Where heart rhythm can be determined and equipment is available, DEFIBRILLATION may be required.