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 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