The application of topical heat for therapeutic purposes has become commonplace in America. It is used by professionals including physical therapists and physicians to treat their patients as well as by individuals within their home or at work. Using computer simulation of two-dimensional heat transfer through the outer tissue layers of the body, the process of heat transfer and temperature gradients within the tissues can be predicted. The objective of this study was to determine the temperature gradient of the muscle layer after applications of heat for less than one-half hour. Finite energy heat sources such as a hot water bottle as well as electric heat constant-temperature sources were evaluated. Applied temperatures were maintained at 50 C or less so not to irritate the skin surface. It was determined in all cases that the temperature of the muscle did not significantly increase within our time frame and actually began to cool after fifteen minutes with the hot water bottle case studies. On the other hand, the temperature of the epidermal-dermal layer, where nerve endings exist, remained at an elevated state of above 40 C for an extended period of time. It is inferred that a heat stimulated response of the neurons may be the cause of muscle relaxation and pain relief when a topical heat source is applied.