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The acute coronary syndrome represents a wide spectrum of conditions from unstable angina pectoris to the acute Q-wave myocardial infarction. During the last fifteen years treatment of acute myocardial infarction has seen radical changes. Large randomised trials have guided the development and intravenous betablockade, aspirin, thrombolytics and direct coronary interventions have been introduced. For the unstable coronary syndrome, mainly unstable angina pectoris and non-Q wave myocardial infarction, however, there has been a lack of large, easily interpretable trials to yield a similar therapeutic progress. Nevertheless oral betablockers, aspirin, heparin and to some extent even coronary interventions have been introduced over the last fifteen years.Patients hospitalised for unstable coronary artery disease are quite heterogeneous with respect to risk for subsequent cardiac events or death and there is a need for risk stratification. Among several methods for risk stratification, continuous on-line vectorcardiography has been shown to provide valuable prognostic information. Previously the presence of ST-VM episodes and 3 or more STC-VM episodes have been used to identify high-risk patients.Among 3791 myocardial infarctions between 1984 and 1991 it was demonstrated that the two-year mortality decreased from 36% in 1984 to 25% in 1991, mainly as a result of declining in-hospital mortality. Nevertheless there was a decline in post discharge mortality as well. No individual factor could be pointed out as the major cause for the decline. It was rather a combination of several factors that improved the long-term prognosis for the infarct patients.Among 3203 patients with unstable angina pectoris or non Q-wave myocardial infarction, admitted between 1988 and 1995, the two year mortality decreased from 30% to 19%. Heparin treatment and acutely performed coronary angiograms were associated with better outcome and the use of these strategies increased over the period, however other factors also played a role for the declining two-year mortality.Among 1248 patients with unstable coronary artery disease, in three different studies, who had undergone 24 hours of continuous online vectorcardiography, different ways of interpreting the ST-monitoring data were assessed. It appeared that ischaemia detected by a ST-maximum >= 144 µV, a ST-area >= 162 µV, presence of ST-VM episodes or presence of >= 3 STC-VM episodes were all indicative of a high risk for death or myocardial within one year. However the consistently best indicator through all three studies was the presence of ST-VM episodes. Furthermore ST-episodes with a high ST-maximum indicated very high risk. ST-VM episodes were prognostically valuable even after adding early invasive treatment and prolonged dalteparin treatment to a substantial part of the population.Against a background of therapeutic changes there is a positive time-trend in the prognosis after acute coronary syndromes. Patients with a non Q-wave myocardial suffer a higher two-year mortality as compared to Q-wave myocardial infarctions and myocardial infarctions differ from unstable angina mainly with a higher very early phase mortality. The detection of ischaem ia by any of several methods with continuous ST-segment monitoring indicates high risk for subsequent death or myocardial infarction, however the detection of ST-episodes is reliable and feasible for clinical practise.