INTRODUCTION: The haemodynamic effects veno-arterial extracorporeal membrane oxygenation (VA-ECMO) remain inadequately understood. We investigated invasive left ventricular (LV) haemodynamics in patients who underwent treatment with an intensive care strategy involving extracorporeal cardiopulmonary resuscitation (ECPR). METHODS: We conducted invasive haemodynamic assessments on 15 patients who underwent ECPR and achieved return of spontaneous circulation. Left ventricular end-diastolic pressure (LVEDP), ejection fraction (LVEF), end-diastolic volume (LVEDV), and stroke work (LVSW) were evaluated using simultaneous invasive left heart catheterization and 3D echocardiography. Paired comparisons between high and low VA-ECMO flow were performed. RESULTS: Invasive haemodynamic studies were performed in 15 patients aged 58 (43,65) years at 3.0 (2.0, 4.0) days after cannulation. Six patients survived the index hospitalization, and 9 expired during the index hospitalization. Among the total cohort, transitioning from the highest VA-ECMO flow (median 4.0 L/min) to the lowest VA-ECMO flow (median 2.0 L/min) led to increases in LVEDV from 85 (68,125) mL to 106 (70,153) mL (p = 0.005) and LVEDP from 14 (8,23) mmHg to 17 (12,30) mmHg (p = 0.001), respectively. Similarly, the LVSW increased from 2051 ± 1525 mL*mmHg at the highest level of VA-ECMO flow to 2627 ± 1559 at the lowest VA-ECMO flow (p = 0.01). CONCLUSION: High VA-ECMO flow significantly reduced LVEDP, LVEDV, and LVSW compared to low VA-ECMO flow.