A Datascope monitoring heart rate
Heart rate, abbreviated HR, was the rate of heartbeats per unit of time in a humanoid. This measurement was described by the Malcorians to be the cardial rate.
In 2256, when Michael Burnham was on approach to the Beacon of Kahless, Danby Connor reported her heart rate at 79 and rising. (DIS: "The Vulcan Hello")
In 2258 of the alternate reality, Doctor Leonard McCoy cautioned a reaction-suffering James T. Kirk that he ought to keep his heart rate down. (Star Trek)
In 2371, during The Doctor's delusion on the USS Voyager's holodeck, he scanned himself and discovered he had a heart rate. (VOY: "Projections")
In 2373, after scanning Lieutenant Tuvok in sickbay, The Doctor noted that his heart rate was at three hundred beats per minute after he was found to be suffering from a severe panic attack on the USS Voyager. It was recalling an apparent memory of a girl falling from a precipice triggered his accelerated heart rate. Tuvok's condition was later discovered to be caused by a memory virus unknowingly placed into his brain by his former crewmate on the USS Excelsior, Lieutenant Commander Dimitri Valtane shortly before he apparently died in 2293. (VOY: "Flashback")