The woman, named locally as Ann Morris, 63, collapsed following a disturbance at the couple's home in a quiet suburb of Troon, South Ayrshire.
She died shortly after being taken to Crosshouse Hospital in Kilmarnock.
Her husband, Fred Morris, 64, is being treated at the hospital for serious head and chest injuries after apparently being stabbed. His condition was described as "serious but stable".
Mrs Morris is believed to have suffered from a heart condition.
Her son, 38, was detained in London after the attack in Troon's Polo Gardens. The incident happened on Friday night.
He was taken into police custody in England and officers from Strathclyde Police were despatched to London to escort him back to Scotland.
Police confirmed that a 38-year-old man has been detained in connection with the death of a 63-year-old woman and the attempted murder of her husband.
Further details of the incident have not yet been released, but police said that it was not a shooting.
Neighbours who live in Fullerton Crescent, opposite the family home, expressed shock at the incident.
Four ambulances and a number of police cars were sent to the scene. A helicopter was also seen circling the area and sniffer dogs were deployed by police.
One neighbour said: "I didn't really known them, but enough to say hello. I think they have been here about 10 years. I have a couple of sons, but I think he is a bit older."
Another neighbour said: "It was quite a commotion. There was a helicopter circling quite low with a spotlight. It was loud; I thought it was going to land.
"There was a lot of activity and I saw the ambulances, then it went quiet. Then at about 2am the men in white suits arrived."
Officers remained at the scene yesterday morning while forensic technicians examined the area, and police officers carried out door-to-door enquiries.
A cordon was extended around the house and neighbouring properties and a grassy expanse in front of Polo Gardens. A white tent was set up directly opposite the house on the grass.
A post-mortem examination is due to be carried out to establish how Mrs Morris died.
A spokeswoman for Strathclyde Police said: "A 38-year-old man is now in custody in England in connection with the incident.
"Officers from Strathclyde Police are travelling down to London to detain the man and bring him back to Strathclyde."
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