During remote video-mediated assistance, instructors often guide workers through problems and instruct them to perform unfamiliar or complex operations. However, the workers' performance might deteriorate due to stress. We argue that informing biofeedback to the instructor, can improve commu- nication and lead to lower stress. This paper presents a thor- ough investigation on mental workload and stress perceived by twenty participants, paired up in an instructor-worker sce- nario, performing remote video-mediated tasks. The interface conditions differ in task, facial and biofeedback communi- cation. Two self-report measures are used to assess mental workload and stress. Results show that pairs reported lower mental workload and stress when instructors are using the biofeedback as compared to using interfaces with facial view. Significant correlations were found on task performance with reducing stress (i.e. increased task engagement and decreased worry) for instructors and declining mental workload (i.e. in- creased performance) for workers. Our findings provide in- sights to advance video-mediated interfaces for remote col- laborative work.