The Garmin Venu 4 and the Apple Watch Ultra 3 are sure to make our best Garmin watches and best Apple Watches lists, respectively, as we wind up the last crop of 2025 releases and head into 2026. As part of my review process, I'm testing its heart rate sensor's accuracy against an industry-standard Polar H10 Bluetooth heart rate monitor, along with using the very accurate Apple Watch Ultra 3 as a 'control' watch during the experiment. The Polar H10 was rated the best heart rate monitor for accuracy by us and many, many others. (Image credit: Lee Bell)I'm using the Polar H10 to test the accuracy of Garmin and Apple's heart rate readings during my 7km lunchtime run. Image 1 of 3 The Polar Flow app, showing a graph from a super-accurate Polar H10 chest-mounted heart rate monitor.