Marine heatwaves (MHWs) have devastating effects on ecosystems and impact regional air-sea CO2 exchange. Yet a global assessment of these regional impacts of MHWs on the air-sea CO2 exchange is missing. Here, we analyze thirty global observation-based air-sea CO2 flux datasets from 1990 to 2019. We observe minimal reduction in global oceanic CO2 uptake during MHWs. Regional variations are evident with the equatorial Pacific experiencing a 31% (spread across datasets: 3-49%) reduction in carbon release, suggesting that MHWs are the dominant drivers of strong air-sea CO2 flux anomalies in this region. In low-to-mid latitudes, MHWs cause a 29% (19-37%) decrease in air-sea CO2 uptake. Reduced dissolved inorganic carbon in the tropics weakens outgassing, while high ocean temperatures diminish uptake in the low-to-mid latitudes. In the North Pacific and Southern Ocean, enhanced carbon uptake occurs during MHWs, but uncertainties in pCO2 datasets limit a comprehensive assessment in these regions.