Simple SummaryIn Japan, cats are popular companion animals. However, the details of the effects of direct communication with cats on the psychological and physiological states of their owners remain unknown. In this study, we conducted a remote-format experiment with 32 cat owners in their homes. Owners were requested to interact with their cats for 10 min in a routine manner. The results showed that interactions with cats decreased the emotional arousal and parasympathetic activity of the owners and increased their heart rates. Positive correlations were also noted between heart rate and cortisol concentration as well as between cortisol and oxytocin concentration. The results of this study indicate that interactions with cats at home has an excitatory effect on the physiological aspects of owners, which is in contrast with findings of previous studies that proposed stress reduction. This explains a new aspect of the mechanism of the health-promoting effects of cat ownership.AbstractInteractions with animals, including cats, is believed to influence human health. However, studies that investigate the psychological and physiological effects of interacting with cats in their household environment are limited. In this remote study, 32 cat owners in Japan participated from June to October 2021. They completed two tasks, each on separate days in their homes: one simulating daily cat communication (Interaction condition) and another with no interactions (Rest condition). We quantified emotions (arousal level and pleasure level) before and after each condition using the Two-Dimensional Mood Scale Short-term as well as salivary cortisol and oxytocin levels of owners using enzyme-linked immune-sorbent assay. Autonomic nervous activity (sympathetic and parasympathetic) was also quantified by heart rate variability analysis. The free interaction with cats decreased emotional arousal and parasympathetic activity, and lead to increased heart rates in owners. There was a positive correlation between heart rate and cortisol concentration, and between cortisol and oxytocin concentration. Furthermore, the frequency of petting the cats was negatively correlated with the rate of change in the parasympathetic activity. In contrast, the parasympathetic nerves in the owners were activated under the Rest condition. Hence, the mechanism of health-enhancing effects of cat ownership includes an arousing effect, in contrast to the previously proposed stress-reduction effect. This result can aid in future developments in cat–human relationship studies. However, a detailed study with a larger sample size is needed to draw definite conclusions.