The primary objective of this study is to propose new treatment algorithm (strategy) for patients with Acute Coronary Syndrome (ACS) and left bundle-branch block (LBBB).

Current recommendations on the treatment of acute coronary syndrome (ACS) dictate urgent reperfusion therapy in the case of evolving myocardial infarction with ST-segment elevation (STEMI). Optimal use of PCI (preferably) or thrombolysis in this situation requires a rapid and correct diagnosis.

According to the ESC'2008 and ACC/AHA'2009 focused update guidelines patients admitted to the hospital within 12 hours after the onset of chest pain with new (or presumably new) left bundle-branch block (LBBB) should be treated like patients having STEMI (class I, level A). However, it is well-known that in patients with concomitant LBBB, the ECG manifestations of acute myocardial injury may be masked.

ACS may occur in a patient with "true old" LBBB (when doctor has/has not an ability to compare the new ECG with the previous one) or (presumably) new LBBB.

There is a high risk of non receiving appropriate therapy or of receiving inappropriate therapy (thrombolysis instead of LMWH/UFH/fondaparinux).

Inclusion Criteria:

• Age 18 - 75 years
• Ischemic discomfort (ie, ischemic chest pain or equivalent) at rest ≥20 minutes within previous 24 hours.
• Any (new, presumably new, or old) LBBB on the prehospital (ambulance) or admission ECG.
• Urgent coronary angiography (followed, when indicated, by PCI), ideally within 90 minutes after admission

Exclusion Criteria:

• all-comers design