Both contemplative practices and social context have been demonstrated beneficial to our mental and bodily well-being, yet little is known about the interplay between the two. This study explores the difference between deep breathing and meditation and how social context influences their effect on vagal nervous activity, before, during, and after the 7.5% carbon dioxide (CO2) enriched air inhalation challenge. We conducted a within-subjects 2 (deep breathing and meditation) by 2 (alone and with a partner) design on 128 college students (84 female). Participants first did contemplative practice either alone or with a partner, then took the CO2 inhalation challenge. Time-domain heart rate variability (HRV) indexed by the root mean square of successive differences between normal heartbeats (RMSSD) increased after the contemplative practice, and no difference between alone group and with-a-partner group was found. In the CO2 stress task, reactivity HRV (the difference between pre-challenge and during-challenge HRV) did not significantly differ between groups. A significant positive relationship was found between subjective distress and RMSSD across the experiment. Results of the current study suggest that we could benefit from solely deep breathing, and it has a similar impact on the vagal tone as meditation.