T-wave alternans is thought to predict the occurrence of ventricular arrhythmias in patients with left ventricular dysfunction and may be the basis of a clinical test for arrhythmia predisposition. Experimental work has associated T-wave alternans to alternating epicardial action potential duration and regions of discordant repolarization alternans has been linked to the induction of re-entry. The occurrence of transmural repolarization alternans was investigated using optical techniques to investigate the link between alternans and ventricular arrhythmia in rabbits with left ventricular dysfunction following myocardial infarction. Optical mapping using the voltage sensitive dye RH237 was used to record action potentials from the transmural surface of left ventricular wedge preparations from normal and post-infarction hearts during a progressive reduction in pacing cycle length at normal (37 °C) and hypothermic temperatures (30 °C). There were no significant differences in baseline transmural electrophysiology between the groups. Post-infarction hearts had a lower threshold for both repolarization alternans (286 vs. 333 bpm, p < 0.05) and ventricular arrhythmias (79 vs. 19%, p < 0.01) during rapid pacing, which was not accounted for by increased transmural discordant alternans. In VF-prone hearts, alternans in optical action potential amplitude was observed and increased until 2:1 block occurred. The degree of optical action potential amplitude alternans but not APD90 alternans was associated with VF inducibility during rapid pacing. Post-infarction hearts are more vulnerable to transmural alternans and ventricular arrhythmias at rapid rates. In some preparations, alternans in optical action potential amplitude was associated with conduction block and VF. The data suggest that changes in optical action potential amplitude and regional block may underlie a mechanism for alternans-associated ventricular arrhythmia in left ventricular dysfunction.