Teaching can be emotionally demanding. The current study investigated how teachers handle demanding situations in class, and how their behavioral and physiological reactions shape their emotions after the lesson. Interpersonal behaviors of 80 secondary school teachers were coded based on video recordings of one real-life lesson. During the lesson, heart rate and cardiac output were recorded continuously as indicator of relative challenge versus threat motivational states. Overall, teachers differed substantially in the number of demanding situations and how they changed their interpersonal behavior and physiological responses. Although teachers' behavioral and physiological changes were not a straightforward predictor of their emotional outcomes, especially teachers with dispositional low agency or communion were at risk of less positive and more negative emotions.