The Heart
The heart is a 
four-chambered pump which moves a 5
to 7.5 liter volume per minute of blood throughout the
circulatory system. As blood enters the atria, each atrium
contracts forcing blood into its respective ventricle. The
strength of ventricular contraction is dependent upon how far the
ventricle is stretched when filled with blood by the atrium. The
higher the pressure, the harder the ventricular contraction. The
rate of contraction times the volume of each stroke constitutes
the cardiac output.
HR (heart rate) x SV (stroke volume) = CO (cardiac output).
four-chambered pump which moves a 5
to 7.5 liter volume per minute of blood throughout the
circulatory system. As blood enters the atria, each atrium
contracts forcing blood into its respective ventricle. The
strength of ventricular contraction is dependent upon how far the
ventricle is stretched when filled with blood by the atrium. The
higher the pressure, the harder the ventricular contraction. The
rate of contraction times the volume of each stroke constitutes
the cardiac output.