Cartoon of pump attached to the heart relative to representative plots of pressure head (pressure difference between ventricle and greater vessel) and flow rate for various pump speeds. Pressure head is a term used for rotary mechanical pumps that quantitatively defines the pressure increase across the pump, that is, the pressure difference between the aorta and left ventricle for an LVAD. (A) A volume displacement pump: flow rate is driven relatively independently of the pressure head. (B) Axial rotary pumps: for a rotary pump the relationship between pressure head and flow rate depends on the pump style and speed. An axial pump with a pressure head, P1 and a specific rotor speed (separate curves), the flow rate through the pump is Q1. If pressure in the aorta increased, for example, through an increased peripheral vascular resistance, this would lead to an increase in pressure head, P2, leading to a decrease in flow rate for the axial pump, Q2. (C) Centrifugal rotary pumps produce high pressures at lower flow rates when compared to axial pumps, with the pressure head being driven by the rotational speed of the impeller, which may go from 1500 to 3000 rpm for pressure heads of 65 to 285 mmHg.