Ranolazine inhibits the late Na+ current and is proposed to reduce angina by decreasing [Na+]i during ischemia, thereby reducing Ca2+ influx via Na+/Ca2+ exchange (NCX). We sought to test this hypothesis and to determine whether oxidative stress during simulated-demand ischemia activates the late Na+ current. We measured [Ca2+]i and [Na+]i in rabbit ventricular myocytes by flow cytometry during metabolic inhibition (MI) with 2 mM cyanide and 0 mM glucose at 37°C plus pacing (P) at 0.5 Hz (P-MI), and in P-MI + 1, 10, or 50 μM ranolazine. In the clinically relevant concentration range (1-10 μM), ranolazine decreased Na+ and Ca2+ loading and the development of myocyte contracture. P-MI caused an increase in fluorescence of the oxidative radical probe CM-H2DCFDA, which was inhibited by the radical scavenger Tiron 20 mM. The NCX inhibitor KB-R7943 (10 μM) and Tiron 20 mM reduced the rise in [Ca2+]i during P-MI and eliminated the effect of 10 μM ranolazine on [Ca2+]i. These results indicate that oxidative stress increases the late Na+ current during MI. Inhibition of the resulting increase in Na+ and Ca2+ loading and contracture seems to account for the observed antiischemia effects of ranolazine.