Cardiac muscle cell fatigue. There are two types of cells within the heart: the cardiomyocytes and the cardiac pacemaker cells. Cardiomyocytes make up the atria (the chambers in which blood enters the heart) and the ventricles (the chambers where blood is collected and pumped out of the heart). These cells must be able to shorten and lengthen their fibers and the fibers must be flexible enough to stretch. These functions are critical to the proper form during the beating of the heart. Cardiac pacemaker cells carry the impulses that are responsible for the beating of the heart. They are distributed throughout the heart
Cardiac neural crest cells the young mice were tagged with enhanced green fluorescent protein (EGFP) and then traced. Tagged CNCCs were concentrated in the cardiac outflow tract, and some were found in the ventricular myocardium. These cells were also shown to be differentiating into cardiomyocytes as the heart grew. Although less were found, these EGFP-labelled CNCCs were still present in the adult heart. When a heart attack was induced, the CNCCs aggregated in the ischemic border zone area (an area of damaged tissue that can still be saved) and helped contribute to the regeneration of the tissue to some extent via differentiation into cardiomyocytes