Extracorporeal membrane oxygenation (ECMO) is an established life-saving therapy for severe acute respiratory distress syndrome and cardiogenic shock, yet it profoundly alters cardiopulmonary physiology and challenges conventional hemodynamic monitoring. Both venovenous (VV) and venoarterial (VA) ECMO modify venous return, ventricular loading conditions, pulmonary vascular resistance, and ventriculo-arterial coupling, leading to complex interactions between native and extracorporeal circulation. As a result, many standard monitoring techniques, particularly indicator-based and pressure-derived methods, lose validity or require careful reinterpretation under ECMO conditions. This review summarizes current evidence on hemodynamic monitoring during VV- and VA-ECMO and critically evaluates commonly used modalities, including echocardiography, invasive arterial pressure monitoring and pulse wave analysis, transpulmonary thermodilution, pulmonary artery catheterization, and microcirculatory monitoring. We highlight configuration-specific pathophysiology, key methodological limitations, and typical sources of misinterpretation for each technique. Particular emphasis is placed on the dissociation between macrocirculatory variables and tissue perfusion, the impact of parallel circulation and flow mixing in VA-ECMO, and the persistence of occult shock despite apparently adequate systemic targets. We propose a physiology-guided, multimodal monitoring framework that integrates pressure, flow, volumetric, and microcirculatory information with serial echocardiography. No single monitoring modality adequately captures the hemodynamic complexity of ECMO patients; instead, informed interpretation of complementary parameters and longitudinal trends is essential to guide individualized clinical decision-making and avoid delayed recognition of ventricular failure or regional hypoperfusion.