Cardiac arrhythmias are a common characteristic of the human diving response. As part of the diving reflex, increased activity of the cardiac parasympathetic nervous system not only regulates the bradycardia, but also is associated with ectopic beats which are characteristic of human heart function during breath-hold dives. Arrhythmias may be accentuated by neural responses to face immersion in cold water, distension of the heart due to central blood shift, and the increasing resistance to left ventricular ejection (afterload) by rising blood pressure. Other changes commonly measured in the electrocardiogram during human breath-hold dives include ST depression, heightened T wave, and a positive U wave following the QRS complex, measurements associated with reduced left ventricular contractility and overall depressed cardiac function during a dive.