Veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is the ultimate therapy for patients with refractory cardiogenic shock. During VA-ECMO, fluid administration is frequent, mostly to treat hypotension, hypovolemia or to enhance cardiac function and ECMO flow by increasing preload [1]. While excessive fluid loading is associated with poor outcome in this setting [[2], [3], [4]], assessing the response to volume expansion remain challenging in patients with VA-ECMO. The tools usually used in critically ill patients failed to be generalized in patients with VA-ECMO. Dynamic markers like pulse pressure variation (PPV), stroke volume variation (SVV) or variations in vena cava diameter during mechanical ventilation [5,6] may be hampered by protective ventilation or the presence of a cannula in inferior vena cava. Therefore, identifying new bedside tools to assess fluid responsiveness after a fluid challenge in patients undergoing VA-ECMO is of importance. Currently, velocity time integral (VTI) is the most used in clinical practice [7,8]. Capillary refill time (CRT) is a simple, rapid and reliable clinical tool for assessing peripheral perfusion at bedside, particularly in shocked patients [7,[9], [10], [11], [12]]. Recently, CRT has been described as a target for management of therapy during septic shock [13]. In patients with acute circulatory failure and without VA-ECMO, the reduction of CRT during passive leg raising has been used as a good diagnostic tool for predicting peripheral perfusion response following fluid loading [14]. However, in patients assisted with VA-ECMO, usefulness of CRT as a diagnostic test has never been evaluated. The aim of our study is to evaluate the usefulness of CRT as a tool to assess the response to fluid challenge in patients undergoing VA-ECMO.