Devices used to measure cardiac activity in standardised behavioural tests could be stressful for the animals and therefore affects their responses. However, to date, the impact of carrying such devices has been poorly evaluated. The present experiment examined the impact of a device used to measure cardiac activity on the behavioural responses of handled and non-handled lambs in a standard human test. Furthermore this study evaluated the variations in heart rate in response to human presence and separation. Twenty-one lambs were separated from their dam 12 h after birth. 11 of them received no additional human contact (non-handled) and 10 received additional contact for 1 week and then 1 day a week until 6 weeks. At 6.5 weeks of age, each lamb was submitted twice to a behavioural test. The procedure comprised three phases: the lamb stayed alone for 2 minutes, then for 2 minutes with the familiar stockperson, and then alone for 2 minutes again. The tested lambs were equipped or not with a cardiac device. The results of this study showed that the device used to measure cardiac activity led to a decrease in vocalisations and locomotion. It had only a limited impact on the behavioural differences between handled and non-handled lambs. It reduced slightly the time spent near the stockperson for the non-handled lambs but no effect on the handled lambs. In summary, the device used to measure cardiac activity led to a general decrease in activity but did not affect the difference between handled and non-handled lambs. Consequently, this method seems to be appropriate for further exploring artificially reared lambs’ perception of humans, with few risks of behavioural alteration.