A good horse-rider \'match\' is important in the context of equine welfare. To quantify the influence of repetition and horse-rider matching on the stress of horses encountering challenging objects, 16 Warmblood horses were ridden in a test-setting on three occasions. On each occasion the horse was ridden by a different rider and was challenged by three objects (A-C). Heart rate (HR), heart rate variability (HRV) of horse and rider, and behaviour score (BS) of the horse were obtained for each object and as a total for each test. The horse-rider interaction was evaluated with each combination and assessed as \'matching\' or \'mismatching\', and the horses were categorised as \'compliant\', \'partly-compliant\' or \'non-compliant\'. Horses exhibited a decreased HR (P=0.015) and a decreased BS (P=0.004) within and across different tests. \'Matching\' horse-rider combinations exhibited less stress as indicated by reduced HR (\'match\' 69+/-10 vs. \'mismatch\' 72+/-9, P=0.001) and BS (\'match\' 1.9+/-1.1 vs. \'mismatch\' 3.8+/-1.4, P=0.017) of the horse. \'Compliant\' (68+/-8, P<0.001) and \'partly-compliant\' (71+/-9, P=0.002) horses had significantly lower HR than \'non-compliant\' (75+/-9) animals. The findings of the study indicate that HR and BS measurements support a subjective \'match\' diagnosis and HR measurement may be a valuable tool in assessing horse compliance.