An Ultrasound Transmission Gel Packet Having Internal Heat Source and Method of Use. The gel packet is sized for a single use, rather than for multiple applications. The gel packets are not pre-heated, but rather are quickly heatable on demand. The gel packets may incorporate a variety of optional internal heating methods, including chemical activation, mechanical agitation and electrical activation, among others. The gel packets are sealed and therefore have extended shelf lives, and further are disposable after use.