Many of the treadmills I've used had HRM (heart rate monitoring) built in and enabled via the metal grips on the forward handlebar area. There are metal grips for HRM on the Matrix S8 treadmills at PF here, but it does not appear to be enabled in the hardware/firmware. The UI screens imply that you can pair a bluetooth HRM with the treadmill itself if you bring one with you. I kinda feel like I'd want demonstrated proof-of-principle before I drop $30+ on a bring-my-own bluetooth HRM. But a BT HRM accessory would also be able to connect to my smrtfon to read through a fitness app. Then the questionable part of the tech is simultaneous pairing of smrtfon to earbuds and HRM, I guess.
Why is HRM important? If you're training for CV (cardiovascular) health, then the AHA (American Heart Association) has by-age recommendations. Generally a strong heart pumps more blood per beat, so you need less BPM (beats per minute) to circulate oxygen effectively. A healthy RHR (resting heart rate) is 60 to 100 BPM, with lower numbers generally implying greater CV health.
Cardio exercise strengthens the heart muscle, of course. Like any muscle training, there are "sweet spots" to maximize training efficiency. For CV exercise, the "sweet spot" (as measured by sustained heart rate in BPM) is called the "aerobic" range, around 85% of max safe(ish) BPM. It's not practical to manually measure BPM while simultaneously making very conscious, concentration-demanding efforts to breathe efficiently and maintain good running posture/form. You can't offload the latter parts - but you can offload HRM to devices to see your moment-to-moment heart rate while adjusting treadmill speed to home in on optimal training heart rate.