The regularity of this motion assures proper blood circulation. Electric current passing through the heart completely upsets this rhythmic motion and results in random muscular contractions. This condition is known as ventricular fibrillation and is nearly always fatal. Energy of the impulse of current is responsible for this hazard and an estimate of the danger threshold for fibrillation is 13.5 watt-seconds. At frequencies above the power range, the primary bodily damage results from dielectric heating.
Heating also occurs from both conduction current and radiation.
The temperature of the human body is maintained remarkably constant by very complex temperature regulating mechanisms. These mechanisms, coordinated by the brain, control temperature by regulating the production and loss of heat. Circulation of bodily fluids contributes to the distribution of the heat. The change in diameter of the blood vessels, for example, regulates the volume and velocity of flow. However, not all areas are equally well regulated, and it is possible for local heating to occur.