Interpersonal physiological entrainment is increasingly argued to underlie rapport, empathy and even team performance. We investigate the presence, temporal development, possible mechanisms and impact of interpersonal heart rate entrainment during collective creative LEGO construction tasks. We observe a statistically significant presence and increase over time of structured entrainment, which relates to the actual unfolding and development of behavioral coordination. Heart rate entrainment does not predict rapport and perceived group competence, but behavioral coordination does. Physiological entrainment, thus, should not be considered a universal unmediated proxy for shared emotions, empathy and collective performance. Behavioral coordination – at least in tasks requiring forms of joint action – seems to be a more informative proxy for both physiological entrainment and collective experience.