In the study of Juven et al.1 the excessive heart rate (HR) increase during the preparation of an exercise test was indicated as a novel predictor of sudden cardiac death. The authors attributed this increase of HR to the mild mental stress caused during the pre-exercise preparation phase and suggested that a localized release of norepinephrin or a faster vagal withdrawal during this mild mental stress could be potentially related to this phenomenon. However, it is difficult to explain why subjects of the tertile with the lower HR increase were surprisingly found to have significantly higher HR at rest. As Juven et al.2 have previously described, the crude risk of sudden death increases linearly with the level of resting HR, a fact that does not agree with the present findings. Furthermore, an impaired autonomic balance should also affect the decrease of HR during the recovery period (post-exercise HR recovery). It would be of great interest to examine whether subjects with excessive increase in HR also have a slower decrease of HR during the recovery period, since HR recovery is a well-documented prognostic factor.3 Although HR recovery predicts all-cause mortality and not sudden cardiac death, the common pathophysiological link makes this comparison intriguing. Finally, the magnitude of the mental stress before a diagnostic test might possibly be exaggerated by the ‘first-time' effect. It would be useful if we knew which of these subjects had undergone an exercise stress test before and how this factor influenced their performance.