Cardiac conductive cells make up only about what fraction of the cells in the atria and ventricles, with the rest being contractile cells?

1. There are two major types of cardiac muscle cells: myocardial contractile cells and myocardial conducting cells. 2. Myocardial contractile cells constitute the bulk, about 99 percent, of the cells in the atria and ventricles. 3. The myocardial conducting cells, which form the heart's conduction system, make up only about 1 percent of the cells. 4. 25 percent, 50 percent, and 75 percent all greatly overstate the small conducting-cell fraction actually found in the heart. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 19 "The Cardiovascular System: The Heart", section 19.2, p. 846_