Inclusion Criteria:  patients with ST-Elevation Myocardial Infarction (STEMI) treated with primary PCI within 12 hours from symptoms onset; patients in sinus rhythm; patients who have read and signed the standard informed consent regarding enrolment in the study.  Exclusion Criteria:  unconscious or intubated patients who are unable to sign the standard informed consent; patients with atrial fibrillation; patients with sinus node dysfunction or atrioventricular block of any degree; frequent premature supraventricular or ventricular contractions; paced ventricular rhythm; patients treated with positive inotropic and chronotropic drugs; history of myocardial infarction or myocardial revascularization (PCI or CABG); patients refusal.