MAX30003 always need 3 leads, how to work with just two?

Question

When using the MAX30003WING board with 3 leads, I get clean ECG data. However, just using two leads, all I seem to get is a lot of noise. Touch the ground lead and the signal is again very good. 
 I am powering it from a battery and sending the received data over a BLE link so the unit is galvanically isolated. I've gone through the datasheet but I don't know why the ground lead should be needed for an isolated system. I was hoping to just need the two leads, but I cannot seem to get that working. Any pointers would be welcome!

GenevaCooper · Accepted Answer

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MAX30003 always need 3 leads, how to work with just two?