There were no systemic failures that led to the death of a woman in a mental health unit, a coroner has found.
Annette Hewins, 51, died in February 2017, less than 24 hours after being detained at Royal Glamorgan Hospital.
Ms Hewins had an undiagnosed 90% blockage of one of her main arteries, which led to sudden cardiac arrest.
Coroner Greame Hughes told an inquest there were failures by individuals involved in her care, but they did not amount to systemic failure.
Ms Hewins was wrongly convicted of starting a fatal fire in 1995.
She was jailed in 1997 over the deaths of 21-year-old Diane Jones and her two daughters - Shauna, two, and Sarah-Jane, 13 months - in Merthyr Tydfil. Her conviction was quashed two years later.
Ms Hewins developed a heroin addiction while in prison.
Inadequate observation records
Mr Hughes found there were failures to carry out clinical observations every four hours as requested by doctors, but those failures did not cause her death.
He also told the Pontypridd inquest that there were inadequate observation records kept in the hospital in Llantrisant, but that appropriate systems were in place.
Ms Hewins regularly took heroin and her withdrawal while in hospital was being treated by addressing the symptoms, rather than by being given an opiate substitute.
The inquest heard that a substitute, such as methodone, could have caused "equally catastrophic results".
Ms Hewins was agitated and displaying psychotic symptoms throughout her time in hospital, but her high blood pressure and other symptoms were treated appropriately, the inquest heard.
The medical cause of her death was coronary arterial atherosclerosis.
In a narrative conclusion, Mr Hughes said that Ms Hewins "likely died as a consequence of a fatal arrhythmia with a background of asymptomatic heart disease".
"It was a likely consequence of the psychological and physiological stresses brought on by her psychosis," he added.
On 7 February 2017, Ms Hewins was detained under the Mental Health Act.
When she was admitted, a doctor said she should be monitored for heroin withdrawal and there should be clinical observations taken every four hours.
The inquest heard that during a 13-hour period, between 03:30 and 16:45 GMT, only one set of observations were recorded.
An opiate substitute would not have been suitable and can be dangerous if administered incorrectly without a full history of the patient's drug use being known, the inquest was told.
There was no written policy for dealing with withdrawal from opiate substances within Cwm Taf Bro Morgannwg University Health Board, but the inquest heard that other health boards do have such policies.
The coroner will write a prevention of future deaths report to the Cwm Taf Bro Morgannwg University Health Board, highlighting concerns he has about record keeping, electocardiogram (ECG) provision and lack of a policy for managing withdrawal from acute opiate dependency.
The coroner also apologised to the family of Ms Hewins for the delay in holding the full inquest.
Ms Hewins' son Joshua, speaking on behalf of the family after the hearing, said they hoped the health board "will act on the lessons learnt from this inquest".
He added: "What happened to mum earlier in her life had a profound effect on her.
"Despite the terrible and wrongful adversity she had to endure, our mum was still the most wonderful loving and caring person who would do anything for her family."