The heart is a contractile organ, but it possesses important properties aside from that of contractility. The functions of rhythmicity, conductivity and irritability are also of fundamental importance in cardiac physiology. The clinician's attention is focused mainly on the contractile function of the heart, since the usual methods of examination, palpation of the apical impulse, auscultation of cardiac sounds and inspection of the heart by the fluoroscope, are means by which this property of the heart may be investigated. Furthermore, impairment of contractile efficiency is the basis for the most frequent manifestation of heart disease, congestive heart failure.
Rhythmicity is the property of stimulus formation, and since the heart is an automatic organ producing its own stimulus, it is obvious that this function is essential in the normal physiologic processes of the heart. If the rhythmic function is so reduced that no stimulus is produced, there is a sudden cessation
NATHANSON MH. RHYTHMIC PROPERTY OF THE HUMAN HEART. Arch Intern Med (Chic). 1943;72(5):613-626. doi:10.1001/archinte.1943.00210110050004