We investigated the expression of emotions while teaching in relation to a teacher's physiological changes. We used polyvagal theory (PVT) to frame the study of teaching in a teacher education program. Donna, a teacher-researcher, experienced high levels of stress and anxiety prior to beginning to teach and throughout the lesson we used her expressed emotions as a focus for this research. We adopted event-oriented inquiry in a study of heart rate, oxygenation of the blood, and expressed emotions. Five events were identified for multilevel analysis in which we used narrative, prosodic analysis, and hermeneutic-phenomenological methods to learn more about the expression of emotions when Donna had: high heart rate (before and while teaching); low blood oxygenation (before and while teaching); and high blood oxygenation (while teaching). What we learned was consistent with the body's monitoring system recognizing social harm and switching to the control of the unmyelinated vagus nerve, thereby shutting down organs and muscles associated with social communication -leading to irregularities in prosody and expression of emotion. In events involving high heart rate and low blood oxygenation the physiological environment was associated with less effective and sometimes confusing patterns in prosody, including intonation, pace of speaking, and pausing. In a low blood oxygenation environment there was evidence of rapid speech and shallow, irregular breathing. In contrast, during an event in which 100% blood oxygenation occurred, prosody was perceived to be conducive to engagement and the teacher expressed positive emotions, such as satisfaction, while teaching.Becoming aware of the purposes of the research and the results we obtained provided the teacher with tools to enact changes to her teaching practice, especially prosody of the voice. We regard it as a high priority to create tools to allow teachers and students, if and as necessary, to ameliorate excess emotions, and change heart rate, oxygenation levels, and breathing patterns. Keywords polyvagal theory . wellness. emotion. prosody. vagus nerve. science teacher education Resumen Investigamos la expresión de las emociones mientras se desarrollan las clases, a través de los cambios psicofisiológicos de los maestros. Utilizamos la teoría polivagal (TPV) para enmarcar el estudio de la enseñanza en un programa de formación de docentes. Donna, una profesora-investigadora, experimentó niveles altos de estrés y ansiedad previo a empezar a dar clase y durante la misma. Implementamos la investigación orientada a eventos para estudiar aquellos relacionados con la frecuencia cardiaca, la oxigenación de la sangre y la expresión de emociones. Se identificaron cinco eventos a los que se les aplicó un análisis multinivel utilizando la narrativa, análisis prosódico y métodos hermenéuticos-fenomenológicos para conocer más acerca la expresión de emociones cuando Donna