Due to the climate change and the increasing heat production of modern pigs (e.g. larger size sows having a larger number of piglets nowadays), pigs are more frequently suffering heat stress. In order to prevent the occurrence of heat stress, there is a need to develop a model which can effectively and efficiently predict the effect of ambient thermal environments on pigs. This study developed a two-node mechanistic model to simulate processes of pig thermoregulation and heat release to an ambient hot environment based on biophysical laws. The two-node model consists of a passive system, which can simulate the heat transfer processes occurring in the body core and at the skin surface, and an active system, which controls the thermoregulatory system based on a positive deviation of core temperature from its reference value under thermal neutral conditions. Vasodilatation and panting in relation to the ambient environment were specifically investigated and mathematically described based on the experimental data from previously published studies. The functions to predict vasodilatation and panting provided a relatively more detailed modelling of the thermo-physiological processes of the pigs compared to the available mechanistic models. The proposed two-node model was expected to effectively predict the thermal status of pigs under various combinations of environmental conditions without further tuning.