INTRODUCTION: There are many ways to indirectly determine the autonomic balance, such as by means of heart rate variability, Valsalva maneuver and active orthostatic stress (AOS). In an AOS test, heart rate (HR) shows a bimodal behavior with a fast HR increase that is explained mainly by vagal withdrawal and a subsequent HR decrease, associate to a vagal reactivation and baroreflex control. Studies have shown a controversial relationship between cardiorespiratory fitness (CRF) and the cardiac autonomic function. PURPOSE: To correlate CRF and the vagal withdrawal response to AOS in Brazilian firefighters. METHODS: We evaluated 26 male military firefighters. AOS test was performed in the morning immediately before the on-duty period. A Heart Rate monitor was used to continuously record HR during AOS. Jackson’s questionnaire was used to estimate CRF. The relative difference between the basal (supine) and peak HR (orthostatic) during AOS (%Δ HR [t0 - tmax]) was calculated to express the vagal withdrawal in relation to basal HR. Due to a nonparametric distribution Spearman correlation test was used (p ≤0,05). RESULTS: We observed a positive correlation (r= 0,597, p<0,01) between %Δ HR (t0 - tmáx) and CRF (Figure 1). CONCLUSION: It was shown that the higher the cardiorespiratory fitness (CRF), the greater the vagal withdrawal as evaluated by %Δ HR (t0 - tmax). Besides being necessary for job-task performance, higher CRF seems to be associated with an improved cardiac autonomic function in firefighters. CRF may be a protective factor for autonomic disordes in firefighters.