<p>Climate changes lead to significant warming of the Southern Ocean. By analyzing observational products and objective analysis data, this study reveals that the Antarctic Intermediate Water (AAIW) shows a zonal asymmetry of heat content changes, resulting from the different regional responses to the large-scale circulations. The heat content changes show significant interannual to decadal variations superimposed on a long-term trend, mainly attributed to the heat redistribution affected by the atmospheric circulations. AAIW in the Indian sector exhibits a significant widespread warming, and AAIW in the southwest Pacific sector presents an unexpected cooling. Warming has increased by 0.4 ZJ (zettajoules, 1 ZJ=10²¹ J) per decade since 1979 in the Indian sector, which is equivalent to the heat gain rate of 0.04 W/m² during 1979–2019 in the Southern Ocean. Upwelling of warm circumpolar deep water driven by upward Ekman pumping, induced by the persistent positive phase of the Southern Annular Mode in recent years, plays a leading role in promoting this warming. The unexpected cooling in the southwest Pacific sector, reaching −0.2 ZJ per decade during 1979–2019, is due to the increasing cold water from sea ice and melting water. An increase of low-pressure anomaly facilitates the shallowing and tilting of isopycnals and the intrusion of cold water into the interior ocean, which is closely associated with the Atlantic multidecadal oscillation. The enhancement of this zonal asymmetry in the AAIW shows an increasing heat content in the Indian sector and a decreasing heat content in the Pacific sector, which implies that the Indian Ocean will become an important potential warming pool in the future.</p>