Energy deposition around the trajectories of ionizing particles with linear energy transfer (LET) of 4, 40, and 400 keV/μm in water and subsequent diffusion of deposited heat is calculated using computational fluid dynamics. Immediately after the deposition of energy by the charged particle, the temperature and pressure in the vicinity of the particle track both increase dramatically, leading to the formation of a thermal spike and a pressure wave. Initially, the region of heat deposition is primarily localized to a region called the “thermal core,” which has dimensions of 0.3, 1, and 3 nm for particles with LETs of 4, 40, and 400 keV/μm, respectively. Instantaneous peak temperatures within the thermal core were 800 °C–2000 °C and peak pressures were about 25 000 atm. This sudden deposition of heat in a localized region leads to a very strong shock wave around the particle trajectory, which is shown to last for a duration of 10−9–10−8s. Even at distances beyond 10 nm away from the particle trajectory, pressures above 100 atm could exist for a duration of up to 10−11s. This local and transient environment, created by the passage of a charged particle in a medium, may lead to new mechanisms of radiation action leading to cell damage, as well as to the development of new radiation detectors.