The first of its kind, FDA-cleared, clinical grade wearable EKG replaces your original Apple Watch band providing access to a 30-second EKG anytime, anywhere.  https://store.alivecor.com/products/kardiaband

AliveCor’s KardiaBand is an FDA-cleared device that checks on-the-spot EKG readings in a Bluetooth-connected strap.  For those who need an on-the-spot more accurate heart rate measurement for medical purposes, this could be an interesting option.  https://www.cnet.com/news/the-apple-watch-now-has-an-fda-cleared-heart-rate-band/