Acidosis is a well recognised consequence of myocardial ischaemia. In this brief article we have reviewed the consequences of acidosis that might be arrhythmogenic. These include early afterdepolarisations and triggered activity, delayed afterdepolarisations, pulsus alternans, and reentry. In each case we have described the evidence that acidosis can provoke such behaviour and then discussed the possible mechanisms and consequences of each behaviour. It seems likely that changes of pH may contribute to arrhythmogenesis during ischaemia by these mechanisms.