Heat's impact on economic growth and aggregate productivity is well-established, but while individual impairments are well-understood as mechanisms, the role of interpersonal dynamics remain unexplored despite the growing prevalence of team-based occupations. In our experiment, programmers were randomly assigned to work individually or in pairs under warm (29°C) or control (24°C) conditions. We found that heat had no effect on individual performance but impaired team performance—not through decreased effort but likely through impaired collaboration. This negative impact was strongest in heterogeneous teams, suggesting heat exacerbates coordination challenges, confirmed by poorer partner evaluations in warm conditions.