At present the extracorporeal systems (heart lung machine, called here HLM) use continuous flow pumps; but this continuous flow is completely different from the pulsatile flow produced by the natural heart, to which the human body is used to. Therefore, in many places, studies on extracorporeal systems using pulsatile blood pumps are going on. If a pulsatile pump replaces the HLM continuous flow pump (one pump system), there is a pulsatile flow in the oxygenator and in the cannula connecting the oxygenator to aorta. Therefore the cannula's inertance influence (which is greater than its compliance influence) and the oxygenator mechanical impedance make necessary high positive and negative peaks in the pump pressure, during the corresponding flow rate increase and decrease phases, to obtain the correct pulsatile flow waveform. But the positive peaks can be obtained while the negative are limited by the blood vapour tension. The consequence is the difficulty to generate the correct flow waveform (necessary to produce the correct aortic pressure waveform) and the possibility to damage the blood. Aim of this invention is the use of an active or passive device, that can be inserted at the end of an HLM, immediately before the connection to aorta (or also immediately after the oxygenator, but using a cannula with a proper distributed compliance in order to compensate its inertance) which allows to have pulsatile flow only in the terminal part of the cannula, so strongly reducing the negative effects of the inertance. This device periodically injects energy to the fluid, so to produce the pulsatility, taking it from an own energy source (active device), or using energy supplied by the continuous flow pump of the HLM (passive device made by a compliance plus an on-off valve).
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