Introduction Postcardiotomy veno-arterial extracorporeal membrane oxygenation (V-A-ECMO) is associated with significant mortality. Identification of patients at very high risk for death is elusive and the decision to initiate V-A-ECMO is based on clinical judgment. The prognostic impact of pre-V-A-ECMO arterial lactate level in these critically ill patients has been herein evaluated. Methods A systematic review was conducted to identify studies on postcardiotomy VA-ECMO for the present individual patient data meta-analysis. Results Overall, 1269 patients selected from 10 studies were included in this analysis. Arterial lactate level at V-A-ECMO initiation was increased in patients who died during the index hospitalization compared to those who survived (9.3 vs 6.6 mmol/L, p < 0.0001). Accordingly, in hospital mortality increased along quintiles of pre-V-A-ECMO arterial lactate level (quintiles: 1, 54.9%; 2, 54.9%; 3, 67.3%; 4, 74.2%; 5, 82.2%, p < 0.0001). The best cut-off for arterial lactate was 6.8 mmol/L (in-hospital mortality, 76.7% vs. 55.7%, p < 0.0001). Multivariable multilevel mixed-effect logistic regression model including arterial lactate level significantly increased the area under the receiver operating characteristics curve (0.731, 95% CI 0.702–0.760 vs 0.679, 95% CI 0.648–0.711, DeLong test p < 0.0001). Classification and regression tree analysis showed the in-hospital mortality was 85.2% in patients aged more than 70 years with pre-V-A-ECMO arterial lactate level ≥6.8 mmol/L. Conclusions Among patients requiring postcardiotomy V-A-ECMO, hyperlactatemia was associated with a marked increase of in-hospital mortality. Arterial lactate may be useful in guiding the decision-making process and the timing of initiation of postcardiotomy V-A-ECMO.