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
Heart rate turbulence the heart. Especially after a heart attack, sympathetic nervous activity tends to be increased. A healthy HRT indicates the presence of a healthy amount of parasympathetic activity, countering sympathetic activity. To take a wider view, however, it may be that a healthy HRT is also an indication of a healthy brain, and is the reason small HRT also predicts a likelihood of death from non- cardiac causes as well as from cardiac causes. Heart rate turbulence Heart rate turbulence (HRT) is the return to equilibrium of heart rate after a premature ventricular contraction (PVC). It consists of a brief speed-up