I-Systole (xa intliziyo izicutha okanye izikhama) yenzeka kuba ii-cells zezihlunu zentliziyo ziya zincipha ngokuncipha. xa zisiba ncinane siyatsho okokuba ziyafingana. Umbane otyhutyha-tyhutyha entliziyweni wenza okokuba ii-cells zifingane. Umbane uqala kwi-sino-atrial node (xa eli gama lishunqulwe lithi-SA Node) I-SA Node liqela lee-cells kwi-atria yangasekunene. ezi cells ziqala i-electrical impulse. Le electrical impulse ibeka umyinge nexesha emazifinyele ngalo ii-cells ze-cardiac muscle. Le ntshukumo ibizwa ngokuba yi-'atrial systole'. Iyakuthi ke yakuhamba i-electrical impulse nge-atrio-ventricular node (Xa eli gama lishunqulwe lithi- eyi-AV Node). I-AV Node yenza okokuba isantya sokubetha kwentliziyo sihle. Ukwehla kwaso ke kwenza okokuba ii-electrical impulses zithathe ixesha ukufika. Yile nto ke le yenza okokuba i-ventricular systole yenzeke emva kwe-atrial systole, itsho yenze okokuba lonke igazi liyishiye i-atria phambi kokuba i-ventricle ifingane (ishwabane).