Abstract: Using daily temperature observations from 2474 stations provided by the National Meteorological Information Center and ERA5 daily reanalysis data for 1981–2023, this study compares the low-frequency (LF) characteristics and dynamic and thermodynamic mechanisms of regional extreme heat events (REHEs) across four subregions of eastern China. The results indicate that summer daily maximum temperatures in all four subregions exhibit substantial 10–30-day oscillations. The evolution of REHEs in all regions is influenced by Rossby wave trains propagating from the northwest (or west) toward the southeast (or east) across Eurasia. Additionally, South China is affected by westward-propagating teleconnection wave trains over the low-latitude western Pacific, whereas the other three regions are influenced by southwestward-propagating East Asia–Pacific (EAP) teleconnection patterns. Accompanied by the dispersion of LF Rossby wave energy from the eastern Atlantic in the mid-to-high latitudes, the eastern part of the mid-latitude North America, the western Atlantic in the mid-latitudes, and the mid-to-low latitude Atlantic toward South China, the Yangtze River Basin, North China, and Northeast China, respectively, key LF circulation systems (i.e., the LF continental highs) that govern REHEs in each region have formed. These systems are deeper over the three northern regions, especially Northeast China, but relatively shallow over South China, where the lower troposphere is shaped by coastal LF cyclonic circulation. The eastward and northward extension of the South Asian High notably affects the other three regions, especially South China, but has a weaker influence on Northeast China. The westward and northward expansion of the Western Pacific Subtropical High strongly influences all four regions, particularly the Yangtze River Basin. Enhanced upper-level convergence and lower-level divergence induce strong subsidence, particularly over South China, resulting in pronounced adiabatic warming. This adiabatic warming, combined with a drier atmosphere, reduced cloud cover, and increased incoming solar radiation, further exacerbates surface heating. Thermodynamic diagnostics indicate that horizontal temperature advection contributes substantially to warming in all regions except South China, with stronger effects in the northern regions. Vertical transport and diabatic heating play important roles during the mid-to-late and early-to-mid stages of REHE development, respectively, especially in South China.