Electric current can damage an individual by thermal heating of the tissues; by disregulating autonomously functioning organ systems, such as the circulatory and respiratory systems; or by once-only or continuing stimulation of the nerves and striated muscles. In the first case, the result is coagulation necrosis, and in the second case life-threatening events can occur, such as arrhythmia or apnea. In the third case, vigorous nerve stimulation can lead to paralysis and vasospasm. Massive muscle contractions due to nerve stimulation or the direct triggering of striated muscles can cause ruptures, ligamentous tears, fractures, and joint dislocations, while prolonged current passing through the thoracic wall may stimulate tetany of the intercostal muscles and diaphragm resulting in asphyxia. This article is confined to a description of thermal or Joule heating of tissues when they form part of an electric circuit and to the effects of direct nerve and muscle stimulation. Other articles discuss nonthermal effects. The injuries a person sustains as the result of an electrical accident depend on a large number of interrelated factors, such as the properties of the electrical power supply, the magnitude and duration of current flow, the current pathway, and skin conditions. It makes a vast difference whether a person is hit by a lightning bolt (extremely high voltage, short current flow) or receives a shock from an electrical power supply (low to high voltage, relatively long current flow). Wide variation in the physical properties of lightning discharges and the discharges from electrical power supplies at home and in industry means that all kinds of injuries can be encountered.