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 precursor to the pulmonary artery. In humans, mutations in Notch most often result in bicuspid aortic valve disease and calcification of the aortic valve. Bone morphogenetic proteins (BMPs) are required for neural crest cell migration into the cardiac cushions (precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries. In neural crest–specific Alk2-deficient embryos, the cardiac cushions of the outflow tract are deficient in cells because of defects in neural crest cell migration. Fibroblast growth factor 8 (FGF8) transcription factors are essential for regulating the addition of