This document discusses diathermy, which uses high frequency electrical current to heat deep tissues for therapeutic purposes. It describes three main forms of diathermy - shortwave, ultrasound, and microwave - and their uses. Surgical diathermy, also called electrosurgery, uses electrical current during surgery to coagulate blood vessels, destroy tissues, and cut tissues without bleeding. It can be monopolar, with one electrode at the surgical site and another elsewhere on the body, or bipolar where both electrodes are on the device near the treatment area. Potential complications include fires caused by sparks igniting gases, burns from faulty equipment or placement of electrodes, and short circuits affecting pacemakers.