Where Does the Cardiac Output Go?

If referring to the cardiac output of the right ventricle, there is only one place for it to go: the lungs. Said another way, 100 percent of the cardiac output from the right ventricle is destined for our lungs. However, the blood pumped out of the left ventricle has many destinations. Under resting and comfortable environmental conditions about 13 percent of the left ventricle’s cardiac output goes to our brain, 4 percent goes to our heart, 20 to 25 percent goes to our kidneys, and 10 percent goes to our skin. The remaining cardiac output from the left ventricle (48 to 53 percent) will then go to the remaining tissue in our body, such as the digestive tract, liver, and pancreas.
 

During exercise, a greater proportion of this cardiac output is routed to working skeletal muscle. This requires some redistribution or stealing ofblood routed to other less active areas at that time, such as our digestive tract. Contrarily, during a big meal and for a few hours afterward, agreater proportion of this cardiac output is routed to the digestive tract, which steals a portion of the blood directed to areas having no immediateneed, such as skeletal muscle.

What Is Cardiac Output?

If we were to measure the amount of blood pumped out of our heart during one heartbeat, whether it be from the left or right ventricle, we would know our stroke volume. Then, if we multiply the stroke volume by our heart rate (heartbeats per minute) we would know the cardiac output:
 

cardiac output = stroke volume (milliliters) × heart rate (beats/min).

Cardiac output is the volume of blood pumped out of the heart, either to the lungs or toward body tissue, in 1 minute. It should not matter which of the two destinations we consider, as they occur simultaneously and will have a similar stroke volume of about 5 to 6 liters (or quarts) per minute. During exercise both heart rate and stroke volume increase, which consequently increases cardiac output. For some of us, cardiac output may increase as much as five to six times during heavy exercise. This allows for more oxygen-rich blood to be delivered to working skeletal muscle.