The aim of this study was to determine the heart rate (HR) and work variables of working cattle dogs during actual mustering exercise using a global positioning satellite (GPS) tracking unit‡ with an integrated HR monitor§. The GPS units allowed tracking of seven different Collie and Kelpie working cattle dogs over a total of ten sessions while employed in their usual role of mustering cattle in three locations in Queensland, Australia. Speed, distance and HR data were collected from the dogs during mustering in a variety of working situations. The working dogs covered distances between 13.3 and 30.2 km during mustering sessions ranging from 1 h 59 min to 4 h 24 min at working speeds of up to 43.7 km h− 1. Working temperatures ranged from 29 to 38°C. HR during working exercise ranged between 120 and 237 bpm and was above 180 bpm for 51–68% of the duration of work sessions. There was a positive linear relationship between speed and HR until HRmax (speed 26.0 km h− 1, 233 ± 4.2 bpm), then HR plateaued (R2 = 97.14%, P < 0.001). This study has documented the type of work done by cattle dogs and has shown that GPS devices and HR monitors can be utilized in field conditions to assess the exercise physiology of dogs.