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Objectives: Carotid artery reactivity (CAR%), involving carotid artery diameter responses to a cold pressor test (CPT), is a noninvasive measure of conduit artery function in humans. This study examined the impact of age and cardiovascular risk factors on the CAR% and the relationship between CAR% and coronary artery vasodilator responses to the CPT. Methods: Ultrasound was used to measure resting and peak carotid artery diameters during the CPT, with CAR% being calculated as the relative change from baseline (%). We compared CAR% between young (n=50, 24±3 years) and older participants (n=44, 61±8 years), and subsequently assessed relationships between CAR% and traditional cardiovascular risk factors in 50 participants (44±21 years). Subsequently, we compared left anterior descending (LAD) artery velocity (using transthoracic Doppler) with carotid artery diameter (i.e. CAR%) during the CPT (n=33, 37±17 years). Results: A significantly larger CAR% was found in young versus older healthy participants (4.1±3.7 versus 1.8±2.6, P<0.001). Participants without cardiovascular risk factors demonstrated a higher CAR% than those with at least two risk factors (2.9±2.9 versus 0.5±2.9, P=0.019). Carotid artery diameter and LAD velocity increased during CPT (P<0.001). Carotid diameter and change in velocity correlated with LAD velocity (r=0.486 and 0.402, P<0.004 and 0.02, respectively). Conclusion: Older age and cardiovascular risk factors are related to lower CAR%, while CAR% shows good correlation with coronary artery responses to the CPT. Therefore, CAR% may represent a valuable technique to assess cardiovascular risk, while CAR% seems to reflect coronary artery vasodilator function.