Frank-Starling law
MCAT glossary · Biological & Biochemical Foundations of Living Systems
Definition
Stroke volume increases with end-diastolic volume (preload); cardiac output = SV × HR.
Frank-Starling law in plain English
The Frank-Starling law explains a neat self-adjusting feature of your heart: the more blood fills a chamber before it squeezes, the harder it squeezes back. Think of stretching a rubber band — pull it back farther and it snaps with more force; heart muscle works similarly, so a fuller chamber (called higher preload, or end-diastolic volume) pumps out more blood per beat (a bigger stroke volume). This matters because it lets your heart automatically match its output to how much blood is returning, no conscious control needed. Your total output per minute (cardiac output) is just how much you pump per beat times how many beats per minute: CO = SV × HR.
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