It does display your last measured heart rate (on both S3 and S2 watch, I can confirm), but not on all of the complications. You need to be using this on a Modular Large, or Utilitarian Large complication to see it working. On all of the smaller complications, you only see the heart icon. I think the reason they decided to make it this way is because the information of when the displayed heart rate was measured is pretty necessary for a feature like this where it's not measured continuously, and there's only enough space on those two complications to do this.
Otherwise you'd have people potentially freaking out seeing just the number like 150 there, even though they stopped running 5 minutes ago - not knowing that the displayed number was actually measured maybe 7 minutes ago.