# Stroke Work and Cardiac Work

In physics, work is the product of force times distance. Therefore, considering a solid object of a given mass, the work done to move the object is the force applied to the object times the distance that the objects moves. In the case of the work done to move a volume of fluid, work is defined as the product of the volume of fluid and the pressure required to move the fluid.

**Stroke work** (SW) refers to the work done by the ventricle to eject a
volume of blood (i.e., stroke volume) into the aorta. The force that is applied to
the volume of blood is the intraventricular pressure. Therefore, ventricular stroke work
can be estimated as the product of stroke volume and mean aortic pressure during ejection.
The use of aortic pressure instead of intraventricular pressure assumes that
kinetic
energy is negligible, which is generally true at resting cardiac outputs. Sometimes this
is simplified to stroke volume (SV) times mean aortic pressure (MAP), although
this will further underestimate the stroke work.

SW = SV × MAP

Stroke work is sometimes used to assess ventricular function. If stroke work is plotted against ventricular preload, the resulting ventricular function curve will appear qualitatively similar to a Frank-Starling curve. Like the Frank-Starling relationship, there will be a family of curves depending upon the inotropic state of the ventricle.

**Cardiac work** is the product of stroke work and
heart rate, which is the equivalent of the triple produce of stroke volume, mean aortic
pressure and heart rate.

*Revised 04/04/2007*