Myocardial infarction results in a massive loss of cardiomyocytes (CMs). Unfortunately, current therapies are unsuccessful in replacing lost CMs, and thus, there is an urgent need for innovative approaches. Here, a nanosystem based on spermine-acetalated dextran (AcDXSp) and encapsulating two drug compounds able to stimulate in vitro CMs proliferation is developed. The nanosystem is coated by deposition of a film constituted by tannic acid (TA) and Fe3+ ions. The coating with TA increases the retention of the nanocarrier in cell co-cultures of CMs and fibroblasts stimulated with transforming growth factor (TGF)-β, due to the high affinity of TA for components of the cardiac extracellular matrix. The system exhibits biocompatibility toward primary CMs and induces their proliferation, as indicated by the two-fold increase of CMs in the active cell cycle. At the same time, the presence of TA synergistically helps contrasting fibrosis by reducing profibrotic genes expression, such as collagen 1 and osteopontin, by approximately 80% compared to the control. Overall, the developed nanosystem demonstrates the capability to stimulate CMs proliferation and reduce fibrosis, showing potential benefits for future in vivo applications.