A mother "begged" doctors in Bristol not to let her baby die after ambulance staff failed to treat her as an emergency, an inquest has heard.
Lacey-Marie Poton was born with a complex heart condition and underwent three operations at Bristol Royal Hospital for Children in 2013.
On July 24, the four-month-old had a stent procedure to improve oxygen flow to her lungs and began vomiting the following day. Lacey-Marie was discharged on July 26 but became "shivering, shaking and pale" on the journey to her home in Fishponds, Bristol, her parents claim.
Her mother, 21 year old Emma Norley, reported Lacey-Marie's condition to the hospital but was told to take her to see a GP as it was "nothing to worry about", Avon Coroner's Court was told.
A receptionist at the GP surgery refused to schedule an appointment as Lacey-Marie appeared too unwell and her parents rushed her to Bristol Royal Hospital for Children.
After an examination, Miss Norley and partner Johnny Poton were informed Lacey-Marie had gastroenteritis and would be discharged.
But just 10 minutes after returning home, Lacey-Marie went into cardiac arrest and Miss Norley had to perform CPR while an ambulance was called.
The inquest heard the ambulance crew did not appreciate Lacey-Marie's "time critical" condition and did not use blue lights on the hospital journey.
Lacey-Marie died in her mother's arms around four hours later. Her inquest is the seventh to take place into the care of child heart patients at the hospital.
"The ambulance arrived within 10 minutes and the paramedics did not think there was anything wrong with Lacey-Marie," Miss Norley told the inquest in a statement.
"I told them I had just performed CPR but they did not seem to understand why I had had to.
"Despite having told the operator on the phone that the patient was a baby, the ambulance did not seem to be properly equipped.
"She was not treated as an emergency and no blue light was used throughout the journey even though Lacey-Marie was still crying and grunting."
Miss Norley said hospital staff were "shouting" at the paramedics when the ambulance arrived as they had not been told Lacey-Marie was coming.
CPR was administered as Lacey-Marie had stopped breathing again but a cardiologist did not arrive for around 15 minutes.
The baby's condition stabilised and she was admitted to the intensive care ward, where she deteriorated and given a 50% chance of survival.
"I was crying my eyes out and begged him (a cardiologist) to save her," Miss Norley said.
"I ran into intensive care and held Lacey-Marie in my arms as she passed away."
A post-mortem examination on Lacey-Marie concluded her death was due to congenital heart disease and Down's Syndrome.
Pathologist Dr Michael Ashworth said the baby was born with a large hole between the right and left side of her heart and "severe narrowing" of blood vessels.
The inquest heard an internal report by South Western Ambulance Service found "the crew did not recognise the time critical nature of the baby and therefore conveyed the patient at normal road speed without a pre-alert to the hospital".
Paramedic Kevin Brown told the hearing, in Flax Bourton, near Bristol, the baby seemed "alert" and a normal colour when he arrived.
"It was decided to go under normal conditions to the hospital," the emergency care assistant said. "Looking back, I may have assumed it due to the fact that the baby was relatively stable and to monitor the baby in the back of the ambulance at high speed with the sirens going is difficult.
"She was obviously poorly. It was obvious we needed to go to hospital. She appeared pale and mottled which is a red flag."
Mr Brown said he felt putting blue lights on may have reduced the four-mile journey time by "one to two minutes" but admitted it could have been longer.
The inquest heard the ambulance took 22 minutes and 19 seconds to transport Lacey-Marie to Bristol Royal Hospital for Children.