Isoprenaline (ISO) can cause chronic heart failure (CHF) by inducing cardiomyocyte apoptosis and oxidative stress. Polysaccharides present in Panax ginseng C. A. Mey. (Ginseng) exhibit potent antioxidant and anti-apoptotic properties, improve hypoxic conditions within the body, and mitigate the damage caused by oxidative stress. This study investigated the activity of ginseng polysaccharides (GP) from different harvest years and their mechanisms of action in alleviating CHF by using in vivo and in vitro experimental validation. In this study, 5-year-old GP (5y-GP) and 15-year-old GP (15y-GP) were obtained via water extraction and alcohol precipitation. Their protective effects against ISO-induced damage in the H9c2 cell line and antioxidant activities were evaluated. Among these, 15y-GP demonstrated strong biological activity. Subsequently, four fractions were eluted from 15y-GP using a DEAE-52 column and the four polysaccharide components were evaluated; of these, component 15y-GP4 exhibited the strongest biological activity. 15y-GP4 was characterized by Fourier-transform infrared and monosaccharide composition analysis, and its preventive effects on ISO-induced CHF were investigated. 15y-GP4 was characterized as an acidic heteropolysaccharide with high glucuronic acid content. It effectively reduced levels of reactive oxygen species, improved mitochondrial function in myocardial cells, and inhibited apoptosis. Furthermore, 15y-GP4 alleviated ISO-induced CHF by downregulating PI3K/AKT/hypoxia-inducible factor-1α (HIF-1α) expression, while upregulating phosphatase 6 regulatory subunit 2 (SAPS2) and protein phosphatase 6 (PP6) catalytic subunit (PPP6C) expression. Immunoprecipitation and co-localization techniques revealed an association between HIF-1α and PP6, with both playing crucial roles in CHF. These results indicate that 15y-GP4 possesses superior bioactivity in preventing CHF, demonstrating broad prospects for the development of CHF applications.