Objective To investigate the effect of immediate hemodilution following venoarterial extracorporeal membrane oxygenation(VA-ECMO) initiation on organ function and treatment strategies in cardiac patients. Methods We retrospectively analyzed the clinical data of 50 patients who received VA-ECMO in the Cardiology Department of First Medical Center of Chinese PLA General Hospital between January 2019 and January 2023. According to the decrease in hematocrit (Hct) after VA-ECMO initiation, the patients were divided into the Hct decrease ≥ 30% (HctΔ30%+) group (n=17) and the Hct decrease < 30% (HctΔ30%-) group (n=33). The two groups were compared in their biomarkers of organ function, blood transfusion, intra-aortic balloon pump (IABP), and continuous renal replacement therapy (CRRT). SPSS statistics 25.0 was used for data analysis. Based on the data type, t test, Mann-Whitney U test, Chi-square test, or Fisher′s exact test was used for inter-group comparisons. Results The proportion of patients aged 65 and over was with 52.9% (9/17) in HctΔ30%+group and 36.4% (12/33) in the HctΔ30%-group. There was no statistically significant difference between the two groups in the general clinical characteristics and clinical indicators before VA-ECMO initiation (P>0.05). After VA-ECMO initiation, the HctΔ30%+ group had greater peaks than the HctΔ30%- group in creatine kinase-myocardial band (CK-MB), aspartic transaminase, and alanine transaminase with statistically significant differences (P<0.05 for all). Compared with HctΔ30%- group, HctΔ30%+ group were more likely to receive treatment of IABP (70.6% vs 36.4%) and CRRT (64.7% vs 18.2%), and had higher dose of transfusion of red cell suspensions and plasma (P<0.05 for all). Conclusion Patients with a Hct decrease≥ 30% after VA-ECMO initiation required greater volume of blood transfusion, was associated with more severe organ damage, and had a higher proportion of those who used adjunct IABP or CRRT. A Hct decrease ≥ 30% after VA-ECMO initiation can serve as a new clinical indicator, providing an important reference for selecting treatment strategies and improving prognosis.