Cardiac optical mapping has traditionally been performed in ex-vivo, motion-arrested hearts. Recently, in-situ cardiac optical mapping has been made possible by both motion correction techniques and long-wavelength voltage sensitive dyes (VSDs). However, VSDs have been observed to wash out quickly from blood-perfused in-situ hearts. In this study, we evaluate the performance of a newly developed VSD, di-5-ANEQ(F)PTEA, relative to an earlier VSD, di-4-ANEQ(F)PTEA. We find that di-5-ANEQ(F)PTEA persists over 3 times longer, produces improved signal-to-noise ratio, and does not prolong loading unacceptably.Clinical Relevance-Optical mapping has provided many insights into cardiac arrhythmias, but has traditionally been limited to ex-vivo preparations. The present findings extend the utility of optical mapping in the more realistic in-vivo setting and may eventually enable its use in patients.