Posted to Twitter, the video has already clocked more than eight million views at the time of writing and the reactions are, well, let's just say the internet is collectively blushing.
Someone even added the score from In The Mood for Love over the video, which is appropriate given Wong Kar-Wai's movie is about repressed sexual attraction.
And if you're wondering if that on-screen and red-carpet chemistry extends to their real lives, no, Isaac and Chastain are both married to other people. Isaac's wife Elvira Lind was even in Venice, standing off to the side of the red-carpet shenanigans.
Clearly, she didn't think anything other than her husband is a very good actor paid to have amazing chemistry with his co-stars.
Isaac (Inside Llewyn Davis, Star Wars) and Chastain (Zero Dark Thirty, Molly's Game) have reportedly been friends since they both attended Julliard almost 20 years ago and we are certainly not suggesting that either of their relationships are headed the way of Bradley Cooper's after that jawdropping Oscar moment with Lady Gaga.
If nothing else, Isaac has a very mischievous smirk on his face.
While it all seems like innocent showmanship for the cameras, it does bode very well for their five-episode series, which was screened at the prestigious film festival.
Adapted from Ingmar Bergman's 1974 Swedish series, Scenes From A Marriage will explore the highs and lows in a modern marriage, following a couple whose relationship descends into despairing loneliness.
It's set to be a powerful character piece, fuelled by two actors with gravitas and – now we know for certain – crackling chemistry.
