Singer Gene Pitney's death at the age of 65 was caused by heart disease.
Singer-songwriter Gene Pitney had been a star since the 1960s
Pitney, whose body was found in the Cardiff Hilton hotel last week, had hardening of the arteries, or coronary artery atherosclerosis.
His death certificate revealed his condition as a book of condolence was opened at Cardiff's St David's Hall, where he had made his last performance.
He was found in his room on Wednesday morning after a standing ovation at St David's Hall the night before.
Pitney, whose hits included Twenty-Four Hours From Tulsa, had played to 1,100 fans in Cardiff in the middle of a 23-date UK tour.
Fans said he had shown no sign of ill health as he chatted with the audience, and read out dedications between songs.
His management company are making arrangements for his body to be flown back to the United States for his funeral.
His death certificate shows his occupation as singer/songwriter and gives his home address in Somers, Connecticut.
He was identified by Geoffrey Clennell, of Hainault, Essex, his former tour manager and friend.
It was Mr Clennell who found Pitney dead in his hotel room, fully clothed after lying down after his show.
The book is open at Cardiff's St David's Hall for the rest of the week
The book of condolence was opened in the foyer on Friday and more than 120 people signed in the first two days.
Cardiff lord mayor Freda Salway, who was the first to sign, said: "I was extremely saddened to hear about the death of Gene Pitney.
"He was a truly iconic figure in the world of music and we were extremely lucky in Cardiff that he visited this city many times to perform at St David's Hall.
"I know that he had many Welsh fans and his performances were always enthusiastically received.
"I wanted to pay my respects by signing this book of condolence, which I know will reflect just how fondly thought of Gene was in Cardiff."
St David's Hall house manager Gareth Griffiths said: "People are going up to it and signing it all the time. It seems to have quite a lot of attention."
"He was a mainstay of our calendar for the past decade or so. He was here every two years."
The book will remain open for the rest of the week.