Cardiac output (CO) is the amount of blood pumped by the heart per minute. It is an important component of how efficiently the heart can meet the bodys demands for the maintenance of adequate tissue perfusion. The bodys demand for oxygen changes, such as during exercise, and the cardiac output is altered by modulating both heart rate (HR) and stroke volume (SV) . Cardiac output is primarily controlled by the oxygen requirement of tissues in the body. The factors affecting stroke volume and heart rate also affect cardiac output. The formula for cardiac output is CO = HR x SV. The normal cardiac output for an adult at rest is about 5 liters per minute.