ECG feature

Do you have dry skin? If you make your finger slightly moist (not wet wet, just a little moisture), does the ECG work?

If you trade Apple Watches with your Husband, does his work for you, and does your's work for him? That would be best test to confirm whether your Apple Watch is working correctly.

Try a forced restart, i.e. hold down both buttons, wait for the Apple logo, let go of the buttons.

Have you set up the ECG in your Health app on the iPhone? Can you open the ECG app at all? Do you get any messages?

So when you open the ECG app on your iPhone it does show a red heart shape and says Hold your finger on the crown?