Automated facial video analysis is useful in numerous health care applications. For example, spatio-temporal analysis of such videos has been previously done for assisting clinicians in the diagnosis of depression. Physiological measures, such as an individual's heart rate, provide very important cues to understand a person's mental health. Unobtrusively estimated heart rate has not been previously used to analyse individuals' mental health. In this paper, we automatically estimate heart rate activity from facial videos. We then study the association of the estimated heart rate activity with the person's mental health, as diagnosed by clinicians. Specifically, from the heart rate activity in response to watching different movies, we classify individuals as either depressed or healthy. The efficacy of the proposed scheme is demonstrated by experimental evaluations on a clinically validated dataset. Our results suggest unobtrusively estimated heart rate to be very effective for depression analysis.