Electrical impulses from your heart muscle (the myocardium) cause your heart to beat (contract). This electrical signal begins in the sinoatrial (SA) node, located at the top of the right atrium. The SA node is sometimes called the heart's "natural pacemaker." When an electrical impulse is released from this natural pacemaker, it causes the atria to contract. The signal then passes through the atrioventricular (AV) node. The AV node checks the signal and sends it through the muscle fibers of the ventricles, causing them to contract.
The SA node sends electrical impulses at a certain rate, but your heart rate may still change depending on physical demands, stress, or hormonal factors.
Texas Heart Institute Heart Information Center
Through this community outreach program, staff members of the Texas Heart Institute (THI) provide
educational information related to the prevention, diagnosis, and treatment of
cardiovascular disease. It is not the intention of THI to provide specific
medical advice, but rather to provide users with information to better
understand their health and their diagnosed disorders. Specific medical advice
will not be provided and THI urges you to visit a qualified physician for
diagnosis and for answers to your questions.