Apple Watch can take an ECG, watch for irregular heart rhythms, flag possible hypertension, and detect signs of sleep apnea — but each of these is enabled one country at a time, and the reason is regulatory.
Heart and respiratory features are treated as health functions, and in most countries that means they require review or clearance from a national health or medical-device regulator before Apple can switch them on. Each regulator has its own process and timeline, so a feature can be live in one country for years before arriving in a neighbouring one. This is fundamentally different from a cosmetic feature that Apple can enable everywhere on day one.
It also explains why availability often expands in waves: when Apple secures clearance in a batch of countries, the changelog can show a long list of regions added for the same feature on the same day.
When the map shows a feature as available in your country, it means Apple lists it as offered there. To actually use it you typically also need a compatible Apple Watch model, an up-to-date watchOS and iOS version, and in some cases your device region must match the supported country. Hardware matters too: some features depend on sensors that only newer Watch models include.
Important: these features are not a substitute for professional medical care or a clinical diagnosis. They are designed to surface possible signs worth discussing with a clinician. Always seek qualified medical advice for health concerns.
Health features change frequently as clearances are granted. The map refreshes daily from Apple's official listings, and the home-page changelog logs every region added or removed.