Ambulance staff have spent longer than 5,000 hours waiting to hand over patients outside north Wales hospitals in the last three months.
The equivalent of 218 days were lost to handover delays at Wrexham Maelor, Ysbyty Glan Clwyd and Ysbyty Gwynedd hospitals between April and June.
Patients should be in the care of hospital staff within 15 minutes.
Betsi Cadwaladr University Health Board and the Welsh Ambulance Service say they are working to improve.
The figures come after coroners highlighted issues with ambulance and emergency department waits following the death of two patients after delays at Wrexham Maelor.
The deaths of 93-year-old Margaret Megan Evans and 46-year-old Ester Wood were said to be accidental and of natural causes respectively, but coroner John Gittins said their wait for treatment was a concern.
Betsi Cadwaldr is currently the worst performing health board in Wales when it comes to the number of lost ambulances hours.
Abertawe Bro Morgannwg University Health Board sits behind with 3,285 lost hours.
A spokesman for Betsi Cadwaldr said its hospitals receive more ambulance arrivals than any other health board in Wales, and that the number of crews ready for their next call within 15 minutes is above the national average.
"We have significantly reduced handovers taking more than an hour over the last month," he said.
"Efforts we are making to improve these rates include increasing our ability to accept patients into our departments, preventing them from waiting in an ambulance, and working with the Welsh Ambulance Service to direct people in need of care to alternative sources."
Andy Long, the Welsh Ambulance Service's area manager for north Wales, added: "Handover delays are of great concern to us and are a symptom of the whole healthcare system being under pressure.
"Our focus is on working with Betsi Cadwaladr to alleviate pressures and keep our resources free flowing."