Cardiac output (CO = HR x SV) is determined by four factors: heart rate, preload (Frank-Starling mechanism), afterload (systemic vascular resistance), and contractility (inotropic state). Optimizing each determinant independently allows targeted therapy: volume for preload, vasopressors/vasodilators for afterload, and inotropes for contractility. Connect Cardiac Output to bedside cues you will reassess first: vitals trends, work of breathing, perfusion, mentation, and pain or ischemic equivalents when relevant. NCLEX items often reward recognizing when subtle instability outweighs reassurance, then selecting nursing actions that protect airway, circulation, and neurologic status before routine tasks.