Abstract Background/objectives Little is known about angiographic and clinical differences in patients presenting with left circumflex artery (LCX)-related ST elevation myocardial infarction (STEMI) and non ST elevation myocardial infarction (NSTEMI). We sought to determine the clinical significance of ST elevations in patients with LCX-related myocardial infarction. Methods and results Between 2005 and 2008 10,503 consecutive patients with acute STEMI and NSTEMI undergoing percutaneous coronary intervention (PCI) were prospectively enrolled into the Euro Heart Survey PCI-Registry. For the present analysis patients with LCX-related STEMI (n = 1100, 54.7%) were compared to those with LCX-related NSTEMI (n = 910, 45.3%). NSTEMI-patients were older, more often female and had a higher incidence of prior cardiac events. Patients with STEMI more frequently presented with shock (8.0 versus 3.9%, P < 0.001) or had been resuscitated (8.5 versus 2.7%, P < 0.0001). TIMI 0–1 before PCI was much more often found among those with STEMI (58.2 versus 25.1%, P < 0.0001). In the univariate analysis there were no significant differences in hospital mortality (STEMI: 4.8%, NSTEMI: 3.5%, P = 0.17), however after adjustment for age, female gender, diabetes and chronic renal failure hospital mortality was significantly higher in STEMI patients (odds ratio 1.71, 95%-CI 1.08–2.72, P < 0.05). Conclusions Over 50% of the patients with LCX-related myocardial infarction treated with PCI had ST elevations in the initial electrocardiogram. STEMIs were more often associated with total vessel occlusions or haemodynamic instability. In-hospital mortality was significantly higher in patients with LCX-related STEMI.