In some cases, when the patient goes into a cardiac arrest, the heart goes into a rhythm that is non-shockable. The only treatment for this, in the initial stages, is to do good quality chest compressions and ventilations. The incidence of reverting asystole back into a rhythm that supports life is less than 6%. For ventricular fibrillation, it’s approximately 40%. The causes of cardiac arrest can be listed as four H’s and four T’s, as a way of helping us remember what they are. And when we are carrying out a cardiac arrest scenario, we will always bear these causes of that cardiac arrest in mind. They are known as reversible causes, and the four H’s are: Hypoxia, hypothermia, hypovolemia and then hypo or hypercalcaemia, natremia, or kalemia, basically, metabolic imbalances. We can also include hyper-ions, I.e. Acidosis in that H. Looking at the four T’s, we’re looking at a cardiac tamponade, a tension pneumothorax, toxins and thromboembolic. The ones that we see most frequently in the pre-hospital setting, are thromboembolic following a myocardial infarct or a large CVA.