The impact of mid-late-life exercise on the aging heart remains unclear, particularly the effects of high-intensity interval training (HIIT) and continuous moderate-intensity training (CMIT). This study was the first to examine cardiac function, tissue characteristics, electrical remodeling, mitochondrial morphology, and homeostasis in old mice subjected to CMIT or HIIT, compared to untrained controls. Our results showed that 8-week HIIT significantly improved the survival rate of old mice. HIIT presented advantages on cardiac function, deposition of collagen fibers, neovascularization, aging biomarkers, and mitochondrial homeostasis. Only CMIT alleviated age-related cardiac hypertrophy. However, CMIT potentially exacerbated adverse cardiac electrical remodeling. Those findings suggested HIIT as a particularly appealing option for clinical application for aging populations.