How to send the ECG signal to the arduino UNO?

Projects General Guidance
4

What, precisely, is generating the waveform (and don't say a human heart...)

It's possible you could just connect the point you're scoping to the A0 analog input of an Uno and run something like:

const uint8_t pinECG = A0;

void setup() 
{
    //don't need to declare A0 as input (default)
    Serial.begin( 115200 );
    
}//setup

void loop() 
{
    uint16_t ecg = analogRead( pinECG );
    float volt = (float)ecg * 5.0 / 1024;
    Serial.println( volt );
    
}//loop