Abstract: An instrument heater for heating a surgical instrument. The instrument heater includes a sheath having an inner and outer wall. The inner wall forms a bore through which the optical scope is inserted. A chemical solution fills the space between the inner and outer wall of the sheath. At one end of the sheath is an activator disk having a chemical substance attached to its surface. When the activator disk is flexed, it ejects the chemical substance and interacts with the chemical solution to initiate an exothermic reaction. The exothermic reaction results in the generation of heat within the sheath, which is transmitted to the surgical instrument. Once the surgical instrument is sufficiently heated to a temperature close to the temperature of a body, the optical scope is inserted into the body. A natural tendency for the instrument to fog up is prevented by the equalizing the temperature of the instrument with the body.