Extra-corporeal membrane oxygenation (ECMO) life support system can provide both cardiac and respiratory support to patients with heart and respiratory failure. It can save time for these patients to regain organ function or to receive transplantation. Both our team and Ince et al. from the Netherland found that the microcirculatory dysfunction is more severe in ECMO non-survivors. The next step of research is to find out the key factors that affect microcirculation in ECMO patients. Because the blood flow supplied by the venoarterial ECMO (VA-ECMO) is directly related to macrocirculation, this study aims to investigate the effect of adjustment of VA-ECMO blood flow on microcirculation. We hope that the results of this study can help the medical team to improve the quality of ECMO care. After evaluation, explanation, and acquisition of agreement, the sublingual microcirculation will be examined within 24 h and at 48 h after placement of VA-ECMO. The VA-ECMO blood flow will be recorded, and the baseline microcirculation will be examined. After the ECMO technician adjusting the ECMO flow, sublingual microcirculation will be examined 2 minutes after each adjustment, and the change of ECMO blood flow will be recorded. When the ECMO team plans to weaning off the ECMO within 72 h, the sublingual microcirculation will be examined. The VA-ECMO blood flow will be reduced by ECMO technician, and sublingual microcirculation will be examined 2 minutes after each adjustment of the blood flow. The ECMO parameters, medications, and clinical data will be recorded, and the prognosis will be followed up on the 28th day.