The sinus node, also known as the sinoatrial (SA) node, is a group of specialized cells located in the right atrium of the heart. Its primary function is to generate electrical impulses that coordinate the rhythm of the heart's contractions. Synonyms for sinus node include sinoatrial node, cardiac pacemaker, and natural pacemaker. Other terms that may be used in reference to the sinus node include the nodal tissue, primary pacemaker, and the sinus mechanism. These synonyms may be used interchangeably in medical literature, as they all refer to the same important structure in the heart.