"normal rhythm" means that something is happening or working in the usual, expected way. It refers to a regular pattern or sequence of events that is considered standard or typical. Full definition
The resulting Cardiogram data then was validated against a group of 51 UCSF patients with AF undergoing a cardioversion procedure, which electrically shocks the heart back into normal rhythm, as well as against a second validation group of 1,617 Health eHeart participants (64 with AF) using the Apple Watch. (ucsf.edu)
The short answer: Consider inviting a celibate person to live with you (short term or long), have single people over for dinner on a regular basis (while your house is still messy and your dishes still dirty), and establish normal rhythms together like running errands or ordering takeout or watching Breaking Bad again. (rachelheldevans.com)
For patients at known risk for this or other heart rhythm abnormalities, an implantable cardioverter - defibrillator, or ICD, may be placed in the chest or abdomen to detect faulty electrical impulses and provide a shock to return normal rhythm. (sciencedaily.com)