SkillsUSA Health Knowledge Practice Test

The tissue that initiates the heartbeat is the sinoatrial node. It sits in the upper wall of the right atrium and contains pacemaker cells that spontaneously depolarize to threshold, generating the first electrical impulse of each heartbeat. This impulse sets the heart’s rhythm and travels through the atria to coordinate their contraction. The impulse then moves to the atrioventricular node, which provides a brief delay, and continues through the Bundle of His and Purkinje fibers to trigger ventricular contraction. So, the sinoatrial node is the natural pacemaker that starts each heartbeat.