In acute myocardial ischemia, the border between the normal and the ischemic myocardium is a region of marked electrical inhomogeneity capable of providing the substrate for re-entry. Premature beats, arising at this border (or elsewhere) may then serve as a “trigger” and initiate re-entry leading to repetitive ventricular premature beats, ventricular tachycardia and/or ventricular fibrillation.