Blood pressureis causedbytheblood onthe walls of the arteries.The heartacts as a pump andwheneach hitcausesincreasedblood pressure.The outputofthe heartblood pressurevariesbetween thetwo measurements:maximumarterial pressure, referred to assistolno, which corresponds to acontractionof the heartinthe overthrowof blood inarteries anddiastolnominimum orarterial pressure, which correspondsto a pressure ofbloodbetween twocontractions.