The practice of inner heat is closely related to the practice of "karmamudrā (las kyi phyag rgya, action seal)", referring to meditative sexual union which leads to the four blisses and is practiced along with inner heat yoga. In some lists, such as that of Milarepa, it is listed as a separate dharma. In other systems, such as that of Gampopa, it is listed as a subset of inner heat yoga. This is because it is considered necessary to have control over the vital energies (through inner heat yoga) in order to be successful in "karmamudrā."