Roller Pump: This is the type most commonly used in clinical perfusion. It has a circular metal housing inside which there is a rotating urn with two rollers fixed at 180 degrees apart. Polyvinyl chloride (PVC) tubing which is resilient, passing through the inner perimeter of the housing is compressed by the rollers effecting non-pulsatile forward flow. The occlusion of the rollers are checked routinely and adjusted to optimum level. Too much occlusioil will cause haemolysis; too less will reduce forward flow.