A 60 year old man presented with unstable angina and electrocardiographic features suggestive of disease of the left anterior descending coronary artery. Angiography showed slight proximal narrowing in this artery with reduced density of contrast that suggested an associated thrombus. Repeat angiography after 24 hours of heparin administration showed the development of a small saccular aneurysm. Three weeks later, after a further episode of unstable angina, angiography showed enlargement of the aneurysm. Although there were no further episodes of angina, repeat angiography three months after the initial event showed further slight enlargement of the aneurysm. It is suggested that the episodes of angina at rest were secondary to embolisation of thrombotic or atheromatous material or both.