Sport horses frequently injure tendons of the lower limb. Tendon boots are commonly applied for structural support and trauma prevention during competitions. However these boots may increase heat stress in the area. Two separate studies were carried out with the aim to improve understanding of the effect of boots on heat around the tendon area. Study 1 measured heat emitted from two types of boots (traditional and perforated, cross over design) covering the superficial digital flexor tendon (SDFT) in 4 horses during a set ridden and lunged exercise test. Study 2, a Field test, measured the effect of boot style (traditional, perforated and open fronted) on skin surface temperature in 131 horses, after completing a cross country event test (either a BE 100 three day event or a CCI* - two day short format event). The Raytek Raynger ST20 (infrared thermometer) was used to measure temperatures during both studies. Boots designed with perforations demonstrated greater heat emissions than traditional (non-perforated) boots (+ 3.5º C, p<0.01). In Study 2 mean tendon surface temperature for perforated type boots (28.0°C) was significantly lower than for traditional boots (32.3°C) and for open fronted tendon boots (31.1°C) (P<0.001). As this was an applied field study, additional environmental factors, such as speed and fitness level of horses, may have influenced results.