Today Apple released watchOS 5.2.1 to the public and this update also includes ECG app support on Apple Watch Series 4 to several more countries:

Croatia

Czech Republic

Iceland

Poland

Slovakia

Irregular heart rhythm notifications are now available in Croatia, Czech Republic, Iceland, Poland and Slovakia. There is also a New Pride face inspired by the rainbow flag. This update also fixes an issue where the numbers on the Explorer face would not appear for some users. watchOS 5.2.1 also Disables accessories with insecure Bluetooth connections