Why is his heartbeat fast and felt clearly when I hug him or keep my hands on his chest?

He is not my boyfriend. We chatted on social media for like couple of months in the lockdown and then no contact for one months... and now after lockdown and no contact for about a month met in person... we have met for about 5 or 6 times now... and everytime we hug his heartbeat is fast. And i can feel this since first meeting only? why?
Why is his heartbeat fast and felt clearly when I hug him or keep my hands on his chest?
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