In the Western industrialized nations, cardiovascular disease, and in particular acute myocardial infarction, is a major cause of morbidity and mortality. Early diagnosis is critical for the prognosis of acute coronary syndromes, but it is often very difficult to make a differential diagnosis of non-ST elevation infarction and other coronary syndromes with elevated troponin levels. This paper makes a retrospective analysis of patients suffering from acute coronary syndrome with elevated troponin levels, excluding significant coronary stenosis. Reference is made to clinical, electrocardiographic and laboratory parameters and an attempt at a prognosis is made. The research involved a comparison of patients who had received percutaneous coronary intervention due to a non-ST elevation infarction. A study was made of 1,437 patients who were admitted to the Cardiology Clinic in Bad Berka between May 2002 and September 2005 suffering from acute thoracic pain and elevated levels of troponin I. Of these, 636 patients fulfilled the initial criteria, in that they were suffering from a non-ST elevation infarction. A coronary angiography was carried out on each patient within 12 hours, after which the patients were divided into two groups: • Patients with acute coronary syndrome without significant stenosis ("ACSOS"; n=127) • Patients with one or more haemodynamically-relevant stenoses that were treated with a percutaneous coronary intervention with stent insertion ("NSTEMI with PCI"; n=509) An analysis of the "ACSOS" and "NSTEMI" groups showed no differences due to age (66.4 vs. 65.9 years old; p=0.69), nicotine consumption (25.3 vs. 22.7%; p=0.75) and left ventricular ejection fraction (56.6 vs. 57.7%; p=0.93). There were also no significant differences when comparing levels of troponin (11.8 vs. 9.7 ng/ml; p=0,95), maximum CK (6.1 vs. 7.1µmol/l; p=0.78) and CKMB (2.7 vs. 2.5%; p=0.76). ST segment depression (21.3 vs. 15.5%; p=0.14) and Q-waves (11.0 vs. 5.3%; p=0.26) during resting ECG were more prevalent in the "ACSOS" group. The comparatively higher amount of negative T-waves in the "ACSOS" group was highly significant (53.5 vs. 40.6%; p=0.009). Highly significant differences were noted in favour of the "ACSOS" group with regard to atrial fibrillation (24.4 vs. 10.8%; p<0.001) and the severity of the initial anginal pain (76.4 vs. 40.2%; p<0.001). CRP levels were also significantly higher in the "ACSOS" group than in the "NTEMI" group (21.9 vs. 16.3mg/l; p=0.004). With respect to cardiovascular risk factors, the NSTEMI group contained highly significantly more patients suffering from diabetes mellitus (39.1 vs. 20.5%; p<0.001), arterial hypertension (89.1 vs. 69.3%; p<0.001) and hyperlipidemia (61.1 vs. 43.3%; p<0.001). Regional wall motion abnormalities were also found to be highly significantly more than in patients with NSTEMI (75.2 vs. 47.2%; p<0.001). Takotsubo cardiomyopathy and virus-induced myocarditis were the most common diseases in the "ACSOS" group. Follow-up examinations showed that the "NSTEMI" group had significantly more myocardial reinfarctions (8.5 vs. 3.4%; p=0.005) and rehospitalisations due to cardiac conditions (70.3 vs. 6.1%; p<0.001). There was no difference in mortality (4.2 vs. 4.9%; p=1.0). In summary, own research and data from previous studies show that the cause of thoracic pain with elevated troponin levels in patients without angiographic evidence of significant coronary stenosis remains unclear in most cases. It was demonstrated that it should not be automatically assumed that a myocardial infarction has taken place based on the severity of the angina attack and on the patient's troponin levels. Classic cardiovascular risk factors such as diabetes mellitus, arterial hypertension and hyperlipidemia increase the likelihood of myocardial infarction, but do not exclude the possibility of another cause. Patients who have undergone NSTEMI have a relatively higher risk of myocardial reinfarction and of rehospitalisation due to cardiac conditions. The increased levels of C-reactive proteins in the "ACSOS" group suggest the presence of inflammatory processes. The considerably higher numbers of patients with atrial fibrillation in the "ACSOS" group should be particularly noted. In a final assessment, this paper showed how the non-invasive diagnostic procedures that are normally used in clinics are not able to clearly distinguish between an NSTEMI and an ACS without evidence of significant coronary stenosis. In conclusion, it should be stressed that it remains essential to continue carrying out coronary angiographies as part of the acute diagnosis of acute coronary syndrome.