Heart Activity 2 - Controlling Cardiac Output

Abstract

Recall that the heart has a group of cells that spontaneously depolarize to act as an intrinsic pacemaker.  This group of cells, called the sinoatrial (SA) node, is located in the right atrium and generally depolarizes about 40 times per minute leading to an intrinsic heart rate (HR) of 40 bpm.  However, most people have an HR greater than 40 bpm at rest and significantly greater during physical activity.  Thus, there must be some external regulation of the heart.