A hospital where a boy died should not be criticised, a coroner has said.
Thomas' mother was not happy with the verdict
Four-month-old Thomas Smith died in Birmingham Children's Hospital in December 2004 following heart surgery.
Birmingham Coroner Aiden Cotter heard Thomas suffered a heart attack after a ventilator failed. A bypass machine was then accidentally switched off.
Recording a narrative verdict, he said the failure to restart the machine had not caused Thomas' death as he was already weakened by the heart attack.
The cause of death was given as a congenital heart defect and cardiac failure while Mr Cotter praised the hospital for giving Thomas every chance of life.
In his written verdict Mr Cotter said the heart attack was "due to a malfunction of the ventilator system".
A narrative verdict is used when a chain of events has led to a person's death.
Thomas' parents said they were disappointed with the verdict and wanted a better explanation of why the ventilator failed.
His mother Lisa Weale, 35, of Longbridge, Birmingham, said Thomas had deserved adequate care and added she was considering further legal action.
"I do feel disappointed that the coroner praised the hospital because I feel that if the ventilator had not failed he would not have had a cardiac arrest," she said.
Earlier she told the city's coroner's court he had been let down in a number of ways.
She said Thomas had undergone successful surgery and been placed on a ventilator. The next day she noticed he had stopped breathing and was later told he had suffered a heart attack.
She said she had been told the ventilator failed leading to Thomas suffering a heart attack, but was not been given an explanation for why it had failed.
Later, a member of staff caused the bypass machine to stop working and staff had not appeared to know how to get it started again.
Mr Cotter said the failure to restart the bypass machine made no difference as irreparable damage had been caused by the heart attack.
He said the hospital should be praised for trying to give Thomas a chance even if it did not work and should not be criticised for not having staff they were not meant to have.
The Birmingham Children's Hospital said the inquest verdict was fair and balanced.