Previously, we have shown that inhibition of glycogen synthase kinase-3b (GSK-3b) protects cardiac myocytes against reperfusion iduced hypercontracture and necrosis. The aim of present study was to analyse that, whether GSK-3b inhibition modulates the ischemia-reperfusion- iduced pH fluctuations and whether this protects cardiac myocytes against reperfusion-iduced Ca2+- oscillations. Methods: Isolated rat cardiac myocytes were exposed to simulated ischemia (anoxic superfusion, no glucose, pH 6.4) for 10 minutes and reperfused with normoxic medium (2.5mM glucose; pH 7.4) for 25 minutes. Cytosolic Ca2+ was measured by the Ca2+-fluorescence indicator Fura-2. The cellular pH was detected by the fluorescence indicator BCECF. SB216763 (6 mM), a specific inhibitor of GSK-3b was applied in the last 8 minutes of ischemia and during the hole time of reperfusion. Results: Simulated ischemia induced an acidosis with pH 6.30 ± 0.07 in cardiac myocytes compared to pH 7.20 ± 0.08 in normoxic controls. During reperfusion, cellular pH abruptly raised to 6.68 ± 0.05 within 12 minutes. However, inhibition of GSK-3b with SB216763 resulted in a slow of cellular pH leading to 6.84 ± 0.05 after 25 minutes of reperfusion. Similarly, SB216763 also markedly reduced the frequency of reperfusion- iduced cytosolic Ca2+-oscillations (10 ± 2.2 vs. 34 ± 4.2 oscillations/min in control). However, SB216763 did not signicantly attenuate the amplitude of the Ca2+-oscillations. Conclusion: The results show that inhibition of GSK-3b decelerates the cellular alkalisation at the beginning of reperfusion and achieves better recovery of pH during further reperfusion. This protects cardiac myocytes against reperfusion- iduced Ca2+-oscillations.