The new Apple Watch 12 and Ultra 4 do heart rate monitoring perfectly

Apple has redesigned the heart rate sensor inside the Apple Watch Series 12 and Ultra 4, and the new system measures heart rate every five seconds throughout the day.

That five-second sampling rate marks a 60-fold jump from Apple’s previous heart rate cadence, made possible by a redesigned electrode with a larger surface area for steadier skin contact during ECG readings.

Apple also rearranged the sensor’s photodiodes into a ring layout that captures light more efficiently, alongside larger, more power-efficient green LEDs built specifically for continuous heart rate tracking throughout the day.

That shift toward near-constant heart rate sensing reflects a wider push across the wearable industry, where health tracking has increasingly become the primary way smartwatch makers differentiate their devices from each other.

Apple frames that push through Kaiann Drance, vice president of worldwide Apple Watch product marketing, who called Series 12 ‘the most advanced health and fitness companion we’ve ever created’ and pointed to the redesigned sensor package behind it.

Heart rate variability and daily guidance

Alongside the heart rate changes, HRV sampling now runs up to 24 times more often than before and feeds two new readings, Recovery HRV and Overall HRV, into a redesigned Vitals app menu.

Those two HRV metrics feed directly into a new Readiness score, which reviews recent activity, vitals, and sleep each morning to suggest whether someone should recover, pace themselves, or push harder that day.

The new S11 chip powers all of this and pairs a power-efficient, always-on processor with CPU, GPU, and neural engine gains borrowed directly from the iPhone 18 Pro’s A20 Pro chip design.

That chip-driven system arrives on the Apple Watch Series 12, which starts at £369/$399, and the Ultra 4, which starts at £749/$799, with pre-orders open now ahead of in-store availability on 18 September.

Beyond the new models, Apple has not detailed whether elements of the redesigned Health Sensing System will reach older Apple Watch models through software, so the accuracy gains remain tied for now to the Series 12 and Ultra 4 hardware.