Cardiovascular diseases claim an estimated 17.9 million lives each year, making them the leading cause of death worldwide and placing an enormous burden on healthcare systems. There is an urgent need for better ways to prevent and treat these diseases and that starts with improving how we study the human heart. This research focuses on developing a more realistic in vitro model of the heart using human stem cell-derived cardiomyocytes (hiPSC-CM) and epicardial adipose tissue (EAT), a unique adipose tissue depot that naturally surrounds the heart. Depending on factors such as age, weight and cardiovascular health, EAT can either support or impair heart function. This thesis investigates how EAT from different patients affects hiPSC-CM, with the bigger aim of more accurately replicating human heart conditions in vitro. This will enhance early-stage drug testing and can form a basis for comparison with disease models. Currently, many drugs are tested in animals like rodents, whose cardiac electrophysiology differs significantly from that of humans and which lack EAT. This can lead to missing important interactions, contributing to drug failures in later clinical trials. A more physiologically relevant in vitro model can significantly benefit the pharmaceutical and biotechnology sectors by improving the accuracy of preclinical testing and reducing costly trial failures. It also supports public health by helping to develop safer, more effective treatments. While the primary users of this model will be researchers, the long-term impact extends to patients, clinicians, the pharmaceutical industry and society as a whole through improved healthcare outcomes.