Although reperfusion is an absolute prerequisite for the survival of ischaemic tissue, it is not necessarily without hazard. Many (but not all) cardiologists are of the opinion that some component of reperfusion may be detrimental and able to inflict injury over and above that attributable to the ischaemia. In this article we define four sequelae of reperfusion which might be designated as "reperfusion injury", we identify possible underlying mechanisms, and consider whether any of these forms of reperfusion injury are of clinical relevance.