Abstract The objective of this study was to determine the effect of heat shock (HS) on the Ca 2+ release and the subsequent development in matured porcine oocytes. Oocytes were matured in vitro and randomly allocated to different heat treatments at 41.5 °C for 1 (HS1h), 2 (HS2h) or 4 h (HS4h). Control groups of oocytes were cultured for 0 or 4 h without HS (39 °C, C0h, C4h). In Experiment 1 (eight replicates), matured oocytes were activated by thimerosal (200 μM, 10 min) following HS. Among all heated groups, maximal intracellular calcium concentration ([Ca 2+] i ) was the highest in the HS2h. The lowest [Ca 2+] i peak among HS groups was observed in the HS4h, but it was higher than that in the non-heated C4h group ( P < 0.05). In Experiment 2 (12 replicates), each matured oocyte was injected with IP 3 (0.5 mM) and the Ca 2+ transient was recorded. The peak [Ca 2+] i in the C4h group was still the lowest among all groups ( P < 0.05). Total Ca 2+ release in HS2h appeared the highest among all treatments, and it was significantly higher than that in HS1h and C4h groups ( P < 0.05). In order to clarify the effect of incubation time in vitro (Experiment 3), matured oocytes were cultured at 39 °C for 0, 2 and 4 h prior to treatment with thimerosal or injected with IP 3 (three replicates). The Ca 2+ release of matured oocytes declined with the prolonged culture ( P < 0.05). Finally, the development of HS-oocytes was evaluated after parthenogenetic activation (Experiment 4, three replicates), and the proportion of embryos developing to the blastocysts were lower ( P < 0.05) in the HS groups (31 ± 7% to 33 ± 1%) than in the control groups (52 ± 11% to 56 ± 9%). We conclude that HS alters the Ca 2+-releasing ability of matured pig oocytes, and that heat-shocked oocytes with greater Ca 2+ release incur a low developmental competence after parthenogenetic activation.