Is there an app for the apple watch 3 to use the ECG app?

The Apple Watch Series 3 does not have the required hardware to be able to take an ECG. It requires an Apple Watch 4 or above.

Bubsteve wrote:

Is there an app for the apple watch 3 for ECG?

What “does not have the required hardware” means here: Apple Watch 3 does not contain the required monitoring electrodes nor the associated electrocardiographic monitoring circuitry, so there’s no source of electrical activity data for any hypothetical ECG-monitoring app.

Same holds for Watch (not) reading blood pressure data. No sphygmomanometer. No sensor. No data. No app.