what does the atria do in the heart
Atrium (heart) The atrium is the upper chamber in which blood enters the heart. There are two atria in the human heart, which receive blood - the left atrium from the lungs, and the right atrium from the venous circulation. The atria receive blood, and when the heart muscle contracts, pump blood to the ventricles. All animals with a closed circulatory system include at least one atrium / auricle (humans have two atria).
Cardiac pacemaker If the SA node does not function properly and is unable to control the heart rate, a group of cells further down the heart will become the ectopic pacemaker of the heart. These cells form the atrioventricular node (or AV node), which is an area between the left atrium and the right ventricle within the atrial septum, will take over the pacemaker responsibility.