We aimed to describe the clinical outcomes of veno-arterial extracorporeal membrane oxygenation (VA-ECMO) therapy in our institution considering clinical context and pH at cannulation. All patients treated by VA-ECMO during the 2005–2020 period with 1 year complete follow-up were included. Our cohort was divided in three groups according to the pH level at cannulation: pH <7 (group 1), pH 7–7.2 (group 2), and pH>7.2 (group 3). Survival was analyzed using Kaplan–Meier method. Association between pH group and survival was estimated using a Cox model. A total of 572 patients were included: 60 patients in group 1, 115 in group 2, and 397 in group 3. Refractory cardiogenic shock (36%) was the main indication. One year survival rates were 13%, 36%, and 43% in groups 1, 2, and 3, respectively (p < 0.001). Death mainly occurred within the first month. The strong correlation between pH and lactates led to propose a simple “three seven rule”: pH <7 and lactate >7 was associated with <7% survival. Veno-arterial extracorporeal membrane oxygenation should be considered with caution in patients with pH <7. Lactates and pH might be important parameters to elaborate a new score to predict survival in this population. The “three seven rule” can be very relevant when facing emergency situations.