The captain (I presume) stated to Moncton Centre that one of the pilots apparently had a heart attack enroute and was being treated onboard. In the checkin with the low sector it almost sounds like he says that he was flying unassisted while the other pilot attended to the ill crewmember. But, I'm not sure, the recording is noisy in that part. The stress level in the Delta transmissions is obviously high.
I've attached edited audio from LiveATC.net in a .zip file that will open on most computers but not on most phones or tablets. The recording for the tower frequency had an open squelch on one of the channels and was unusable.
From AV Herald:
Incident: Delta B772 near Moncton on May 21st 2020, first officer incapacitated
By Simon Hradecky, created Monday, May 25th 2020 21:00Z, last updated Monday, May 25th 2020 21:00Z
A Delta Airlines Boeing 777-200, registration N702DN performing flight DL-3343 from Frankfurt/Main (Germany) to Chicago O'Hare,IL (USA), was enroute at FL400 about 60nm northnortheast of Moncton,NB (Canada) when the first officer became incapacitated. The captain called the relief first officer to the flight deck and diverted the aircraft to Moncton for a safe landing about 15 minutes later. The first officer was taken to a hospital.
The Canadian TSB reported, the captain summoned the relief first officer to the flight deck and together they provided first aid to the first officer including the use of an automated external defibrillator to stabilize the first officer. After diversion to and landing in Moncton the first officer was transported for medical treatment. The condition of the first officer is currently unknown.
Incident: Delta B772 near Moncton on May 21st 2020, first officer incapacitated