Auduino MegaADK dual serial port comms

Hello,
I have an Arduino Mega ADK board connected to the PC via the normal square serial connector.

I also have a nordic semiconductor NRF52 board
This is receiving heart rate data from a chest strap via ANT+, and sending the values on its own micro USB serial port @ 115,200 baud, 8 data bits, 1 stop bit, no parity, no flow control.
(This is working correctly, using Putty terminal emulator on the PC and plugging the NRF52 directly into a PC USB port, I can see the steam of heart rate data.)

Next step is to get the data across to the arduino.
I’ve connected the NRF52’s micro USB port to the Arduino’s second serial port (attached), but can’t get any data.
Also tried cutting a USB cable in half and connecting to pins 18,19+gnd, but no data.

Can you please help me to get going?
Many thanks,
Phil.

(deleted)

Thanks for your reply.
My misunderstanding, I thought USB was just serial with higher speed capabilities.
I was using the standard serial passthrough code from the arduino library, which explains why nothing worked!

Could you please offer any basic guidance as to how I can get data from the NRF52 to the arduino?
Many thanks for your help.
Phil

Get a data sheet for your board, and find out how it can communicate with an Arduino.

For serial communication I'd recommend to use e.g. Serial1, not the Serial which is also used for uploading sketches and debugging. For high data rates SPI may be a better communication choice, depending on what the shield offers.