This thesis focuses on the pharmacological treatment of heart failure with reduced ejection fraction (HFrEF). It examines the four main drug classes known as the “Fantastic Four”: RAAS inhibitors, beta-blockers, mineralocorticoid receptor antagonists, and SGLT2 inhibitors. The mechanisms of action and clinical benefits of these therapies are discussed. Evidence from major clinical trials is briefly reviewed. These medications significantly reduce mortality and hospitalization in patients with HFrEF. The study emphasizes the importance of early and combined use of these drugs in clinical practice.