There were 1323 deaths due to ischaemic heart disease in Belfast from 20 July 1981 to 19 July 1982. Some 496 (37%) of these were in persons aged less than 70 years. By World Health Organisation criteria 247 (19%) of these deaths were classified as definite myocardial infarction and 749 (57%) as possible myocardial infarction. Dyspnoea, collapse, and typical pain were the main symptoms at the onset of the fatal attack. In hospital only 12% of deaths in persons aged less than 70 years and 14% of those aged greater than or equal to 70 years were due to presumed primary rhythm disturbance, whereas outside hospital these proportions were 78% and 59% respectively. The median survival time was 84 minutes and was shortest in men aged less than 70 years (62 minutes). Outside hospital a relative was the most likely aid sought initially (70%) and the median delay time from onset of symptoms to calling for medical aid was eight minutes. Among 128 witnessed deaths in persons aged less than 70 years occurring outside hospital due to presumed primary rhythm disturbance the median survival time was 8 X 25 minutes. Improvements in facilities available for resuscitation including public education could result in the prevention of a proportion of deaths caused by primary rhythm disturbances.