Heart rate node, where the faster pacemaker cells driving the self-generated rhythmic firing and responsible for the heart's autorhythmicity are located. For endurance athletes at the elite level, it is not unusual to have a resting heart rate between 33 and 50 bpm. The "maximum heart rate" (HR) is the highest heart rate an individual can achieve without severe problems through exercise stress, and generally decreases with age. Since HR varies by individual, the most accurate way of measuring any single person's HR is via a cardiac stress test. In this test, a person is subjected to controlled physiologic stress (generally by
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