Diastole and systole
(a) During cardiac diastole, the heart muscle is relaxed and blood flows into the heart. (b) During atrial systole, the atria contract, pushing blood into the ventricles. (c) During atrial diastole, the ventricles contract, forcing blood out of the heart.
Source
Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:
"OpenStax College, Mammalian Heart and Blood Vessels. October 17, 2013."
http://cnx.org/content/m44805/latest/Figure_40_03_03.jpg
OpenStax CNX
CC BY 3.0.
