A killer husband told a jury how he developed tunnel vision and snapped, stabbing his jazz singer wife in the heart after she told him she was having an affair.

Mark Arthur, who denies murdering his wife Heather, said his blood pressure rose and he could hear his own heart racing in the moments after she launched a personal ''tirade'' about his character.

Newcastle Crown Court has heard the former British Airways manager planned in the weeks before she was killed to leave her husband for jazz saxophonist Paul Gowland, 44, after they fell in love.

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The 50-year-old defendant, who admits manslaughter after knifing her in the study of their home in Gosforth, Newcastle, last April, said he developed tunnel vision and started to see pink after she said she was seeing someone else and wanted to leave him.

He wept in the witness box as he recalled the row, stabbing her, trying to perform CPR then running to his GP surgery in his boxer shorts to get medical help.

Arthur, a self-employed IT consultant, was anxious that morning as he was due to get test results from the doctor after he became concerned he had cancer.

As he discussed with her about attending the appointment with him, she began to say ''preposterous'' things about him, he said.

''She launched into this tirade which got very personal very quickly,'' he said.

''She started saying that I was manipulative and controlling, that I never showed her any affection.''

Arthur told the court he asked his wife to stop being hurtful.

''I asked her why she was saying these things. That's when she turned to me and said she was having an affair.''

Arthur said that was the first time he had heard she was seeing someone else, and he had not suspected it before.

''She said she was going to seek a divorce, she said that the house was going to be sold and she would keep most of the money.''

Arthur said he tried to picture what the future would be like after the break-up of their 30-year relationship and it got ''worse and worse and worse''.

He added: ''I could not understand why somebody I loved this much was attacking me so viciously.''

He told the court: ''The shock of all of this coming out in the way that it did just made me very, very angry and the anger came out.

''I remember my blood pressure went through the roof, I could actually hear my own heart beat while I was trying to picture these things Heather was saying to me.

''My heart was beating so fast I don't know how I did not have a heart attack. It was racing.

''I do remember I developed a sort of tunnel vision, I could only see clearly in this very small area straight ahead in front of my eyes.

''Everything was out of focus and pink.

''Suddenly all the things that had been going on in the past couple of weeks clicked into place and my whole world collapsed in a second. Just like that.

''Everything that I thought I knew has just gone.''

Still sitting at his desk in his dressing gown, he went on to stab his 50-year-old wife.

He said: ''I picked up the knife which must have been right on the desk and then I remember both of Heather's hands wrapped around my hand and at this point I am pulling the knife away from Heather.''

With his voice breaking, he added: ''In the end I remember standing up and pushing forwards and that is when Heather got stabbed.''

He said prior to picking up the knife he had not intended to harm her.

He made attempts to revive his wife but they failed.

''When I looked in Heather's eyes I thought she was dead and I just spiralled into despair and my brain was shutting down.

''I couldn't believe what had just happened. I was not sure what was going on was real.''

He was arrested at the GPs surgery where he ran to get help and in subsequent interviews he struggled to remember what had happened, he said.

Joanna Greenberg QC, defending, asked: ''Did you realise you had been responsible for Heather's death?''

He replied: ''My brain just wouldn't go there.''

She asked: ''Up until Heather confronted you with what you describe as the destruction of your whole life, would you ever have contemplated laying a finger on her?''

''No,'' he replied.

The trial continues.