Cardiac Output

Stroke Volume (SV)

Amount of blood pumped out of a ventricle with each contraction.

Cardiac Output (CO)

Amount of blood pumped by a ventricle in 1 minute.

Cardiac Output Formula

CO = SV × HR

Stroke Volume Formula

SV = EDV − ESV

Heart Rate (HR)

Number of heartbeats per minute.

End-Diastolic Volume (EDV)

Amount of blood in the ventricle just before contraction.

End-Systolic Volume (ESV)

Amount of blood remaining in the ventricle after contraction.

Normal Stroke Volume

About 70–80 mL per contraction.

Preload

The amount of stretch in the ventricular walls before contraction.

Frank-Starling Law

Increased ventricular stretch (preload) causes increased stroke volume.

Venous Return

The amount of blood returning to the heart.

How does increased preload affect stroke volume?

Increased preload increases stroke volume.

How does increased stroke volume affect cardiac output?

Increased stroke volume increases cardiac output.

How does heart rate affect cardiac output?

As heart rate increases, cardiac output generally increases if stroke volume stays the same.

Athlete's Resting Heart Rate

An athlete may have a lower resting heart rate because a stronger heart pumps more blood with each beat.

Why can a person with heart failure have a higher heart rate?

Lower stroke volume may cause the heart to beat faster to maintain cardiac output.

Example: SV 80 mL and HR 70 bpm

CO = 80 × 70 = 5,600 mL/min = 5.6 L/min.