This cardiology chapter distills ten pivotal studies that drive everyday decisions across prevention, arrhythmias, acute coronary syndromes, heart failure, and mental health in cardiac care. For hypertension, ASCOT-BPLA redirects first-line therapy toward CCB/ACE-inhibitor strategies, while ASCOT-LLA and DASH reinforce complementary lipid and lifestyle interventions; ASCEND clarifies the narrow risk–benefit balance of aspirin for primary prevention in diabetes. In atrial fibrillation, ROCKET-AF supports DOAC use over warfarin alternatives, and AFFIRM defines when rate control is preferred while underscoring continuous anticoagulation. In NSTE-ACS, CURE establishes dual antiplatelet therapy with clopidogrel. Beyond ischemia, SADHART demonstrates the cardiovascular safety of sertraline after MI and its efficacy in recurrent depression. For ventricular remodeling and decompensation, SAVE shows survival gains with early ACE inhibition post-MI, and DOSE guides pragmatic diuretic dosing and delivery in ADHF. Together, these trials form a core evidence base for modern cardiology practice, shaping both outpatient prevention strategies and acute inpatient management.