Background: Patients with acute coronary syndrome with signs of ongoing myocardial ischaemia at first medical contact should be indicated for immediate invasive treatment. Aim: To assess the incidence, treatment strategies and outcomes of acute coronary syndrome in a large unselected cohort of patients with respect to the signs of ongoing myocardial ischaemia. Methods: The CZECH-3 registry included 1754 consecutive patients admitted for suspected acute coronary syndrome to 43 hospitals during a 2-month period in the autumn of 2015. Acute coronary syndrome with ongoing myocardial ischaemia was defined by the presence of persistent/recurrent chest pain/dyspnoea and at least one of the following: persistent ST-segment elevation or depression, bundle branch block, haemodynamic or electric instability due to suspected ischaemia. Major adverse cardiac events (death, reinfarction, stroke, unexpected revascularisation, stent thrombosis) and severe bleeding according to Bleeding Academic Research Consortium criteria were evaluated at 30 days. Results: Acute coronary syndrome was ruled out during the hospital stay in 434 (24.7%) patients. Out of 1280 patients with confirmed acute coronary syndrome, 732 (57%) had clinical signs of ongoing myocardial ischaemia at first medical contact. Coronary angiography was performed in 94.7% of patients with confirmed acute coronary syndrome with ongoing myocardial ischaemia and 89% of patients with confirmed acute coronary syndrome without ongoing myocardial ischaemia (P<0.001). The major adverse cardiac event rate was 9.8% for patients with confirmed acute coronary syndrome with ongoing myocardial ischaemia and 5.5% for patients without ongoing myocardial ischaemia (P=0.005), the 30-day severe bleeding rate was 1.6% and 1.5% (P=1.0). Patients with ongoing myocardial ischaemia admitted to regional hospitals had higher major adverse cardiac event rates compared with patients admitted directly to cardiocentres with percutaneous coronary intervention capability (13.3% vs. 8.2%, P=0.034). Conclusions: Ongoing myocardial ischaemia was present in more than half of patients hospitalised with acute coronary syndrome. These very high-risk patients may benefit from direct admission to percutaneous coronary intervention-capable centres.