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 and GATA families of molecules. In addition to these signaling pathways, these processes are also mediated by environmental factors including blood flow, shear stress, and blood pressure. The CNCCs interact with the cardiogenic mesoderm cells of the primary and secondary heart fields, which are derived from the cardiac crescent and will give rise to the endocardium, myocardium, and epicardium. The CNCCs themselves are the precursors to vascular smooth muscle cells and cardiac neurons. For example, CNCCs are required for the formation of the aorticopulmonary septum (APS) that directs cardiac outflow into two tracts: the pulmonary trunk and the aorta of