Two paramedics and a doctor battled in vain to save the life of a US tourist who suffered a heart attack during a scuba dive trip.

The medics happened to be onboard the Tenacity during the excursion to North Rock when 52-year-old James Norman Miller fell ill on Wednesday.

Graham Maddocks, owner of boat operator Triangle Dive, explained they helped crew members administer CPR to the victim, but it is believed Mr. Miller died almost instantly.

"It was a 35-minute dive to North Rock and the dive was almost over. He was coming back to the boat and was only a short distance from the back of the boat when his dive buddy signalled to me that he was in distress.

"By the time he got back to the boat, it was all over, " said Mr. Maddocks.

He described Mr. Miller, from Sharpsville, Indiana, as a high-ranking diver who was very competent and had participated in a night-time diving expedition the previous evening. He was a passenger from the Norwegian Crown cruise ship along with his wife, who was aboard that vessel when the incident occurred.

The crew from the Tenacity, which was 12 miles offshore, called for assistance just after 4 p.m.

According to Bermuda Maritime Operations Centre, the patient was taken to Spanish Point Boat Club on a Maritime Police boat, and transferred by ambulance to King Edward VII Memorial Hospital after arriving onshore at 5.07 p.m. He was certified dead on arrival.