<P> Cardiac output (CO, also denoted by the symbols Q (\ displaystyle Q) and Q _̇ c (\ displaystyle (\ dot (Q)) _ (c))), is a term used in cardiac physiology that describes the volume of blood being pumped by the heart, in particular by the left or right ventricle, per unit time . Cardiac output is the product of the heart rate (HR), which is the number of heart beats per minute, and the stroke volume (SV), which is the volume of blood pumped from the ventricle per beat; thus, CO = HR × SV . Cardiac output values can be represented using many physical units, such as dm / min, but is usually denoted as L / min . In a subject weighing 70 kg, the cardiac output at rest would be around 5 L / min; assuming a heart rate of 70 beats / min, the stroke volume would be approximately 70 mL . </P> <P> Because cardiac output is related to the quantity of blood delivered to various parts of the body, it can be used as an important indicator of how efficiently the heart can meet the body's demands for perfusion . For instance, exercise requires a higher level of CO to support increased muscle activity . In heart failure, CO may be insufficient to even support simple activities of daily living and cannot increase sufficiently to match the higher metabolic demands stemming from even moderate exercise . </P>

Which of the following is the best indicator of cardiac output
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