Verge review calls it "remarkably small-time" and "a weird thing to hype as much as it's been hyped" -
"But here’s the thing — it doesn’t happen in real time. I had assumed that sending a heartbeat meant that my recipient would just start feeling my heart on their wrist like some sort of cosmic love connection, but that’s not how it works. Instead, you get a regular notification which sends you into the Digital Touch canvas, where the message plays back: the taps come through, the drawings draw themselves, the heartbeats beat."