Update: The ECG function is now officially supported in Europe and Hong Kong. The full list of countries where the function will be working with the roll-out of watchOS 5.2 is: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Guam, Hong Kong, Hungary, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Puerto Rico, Romania, Spain, Sweden, Switzerland, UK, US and US Virgin Islands.
Several iPhone users outside of the U.S. reported that after installing iOS 12.2, pushed out on March 25, they started seeing ECG screens. MacRumors reports that this could be an early indication that the ECG functionality could expand to other countries outside of the U.S., once watchOS 5.2 will be pushed out.
Furthermore, the Health app’s instructions is clearly mentioning that for non-US regions, “the ECG app is available on Apple Watch Series 4 with watchOS 5.2 paired with iPhone 5s or iOS 12.2 or later”. It’s not clear whether it will be just the U.K., or other European countries, or regions. However, a different report mentions that the ECG feature in iOS 12.2 has now earned the CE symbol, which could indicate an EU-wide roll-out and availability.
It is also unknown when Apple will be rolling out watchOS 5.2, but the list of countries in which the ECG function is available has not been amended.