In more than 70% of the cases thrombi in the coronary arteries responsible for myocardial infarction can be dissolved by intracoronary injection of a fibrinolytic agent. For the left ventricular function to improve thrombolysis must be performed within 4 hours of thrombus formation; when performed later, results are inconstant. The risks of arteriography and thrombolysis (mostly dysrhythmias and haemorrhage) are real but acceptable. The mortality rate is lower than with conventional treatment. Improvement in left ventricular global ejection fraction is more pronounced in cases with collateral circulation and when thrombolysis is performed at an early stage. Thrombosis recurs within a few days in 15-20% of the cases. This can be prevented by aorto-coronary bypass or transluminal dilation of the stenotic vessel with a balloon catheter, either of these being carried out very early in cases with tight stenosis or delayed when the stenosis is significant but not life-threatening. A multicentre trial should be set up to find out whether intracoronary thrombolysis improves long-term survival and prevents late complications. But even if this were true, it should still be demonstrated that the method is as effective and safe as intravenous thrombolysis.