A patient with acute anterior myocardial infarction was treated with intracoronary thrombolysis. At cardiac catheterisation the first contrast injection into the left coronary artery dislodged some of the thrombus occluding the left anterior descending coronary artery. The thrombus embolised into the circumflex artery where fortunately it fragmented without causing occlusion. The risk of detachment of thrombus should be borne in mind when angiography and thrombolytic treatment are considered in acute myocardial infarction.