Abstract A 61-year-old man with unstable angina underwent emergency angioplasty of a proximal left anterior descending coronary stenosis. This was successful but a major first septal branch involved in the stensis was occluded following the procedure. Recovery was uncomplicated, however, without chest pain or other evidence of myocardial infarction. Predischarge treadmill stress testing was negative for ischaemia but two hours afterwasrds abrupt coronary occlusion required a second emergency angioplasty procedure. Recanalization of the left anterior descending artery was achieved and the first septal branch was shown to be fully patent. Spasm probably accounted for the side branch occlusion which complicated the first procedure but the mechanism of the abrupt coronary occlusion following stress-testing is unclear.