Selwa Romedan was just 21 when she died days after having her daughter Sadenselwa, at St James' Hospital in Leeds, in September 2016.
An inquest held into Selwa's death found the new mum was suffering from an undiagnosed heart condition causing narrowing of a valve, and had been experiencing chest pains and shortness of breath in the days before giving birth.
Doctors told Miss Romedan she was anaemic and gave her a blood transfusion.
But Leeds Teaching Hospitals NHS Foundation Trust has now apologised after an investigation found she could have survived if her mitral valve stenosis condition had been diagnosed and treated sooner.
Miss Romedan's partner Muhanad Adem told coroners how his daughter's birth was the happiest day of their lives, but one which was ultimately followed by tragedy.
He said: "I cried with happiness when Saden was born and she was put in my arms."
Less than a day after the birth, the new mum was brought back to St James's for a transfusion and was told she was just tired and needed to rest.
She was discharged but readmitted after collapsing in the early hours of September 25, 2016, after getting up to feed her daughter and telling Mr Adem she could not breathe.
Mr Adem said: "She said 'I am dying, I am going from you'. And she just collapsed - she fell down and I fell down with her."
The forklift truck driver, who had fled Eritrea with his partner and resttled in Leeds after being granted asylum, was later told Miss Romedan had died.
He said: "It makes it worse knowing that they could have done something to save her. We came here to be safe and I put my trust in them."
"I didn't want to believe it at first and I didn't, not until I saw her. I kissed her and told her I loved her and I promised to look after the daughter she had given to me".
Mr Adem now devotes his life to looking after his daughter.
-> Leeds student Afrika Yearwood ended life after 'being refused adult mental health service support', inquest hearsDr Yvette Oade, acting chief executive at the NHS Trust, said: "Miss Romedan died in tragic circumstances in 2016 due to complications from an undiagnosed serious heart condition that remained asymptomatic during her pregnancy and subsequent delivery.
"At the time, we undertook a serious incident investigation to help us understand the cause and identify learning from this. This concluded that, if the condition had been diagnosed earlier, then treatment would have been provided for this.
"Had this procedure been performed then Miss Romedan may have survived.
"We understand the deep pain caused to Miss Romedan's partner and family and reiterate our sincere apologies and condolences for their loss."
Mr Adem added: "I know I have to live my life for my daughter. Saden is two and a half now and a strong, happy girl just like her mother. I have to be mum, dad, everything to her and give her all the chances we didn't get.
"It's very difficult though. I have no family around me. I have had to take time off work to care for her.
"I have a beautiful relationship with my daughter and I am so thankful for that, but I never imagined life would be like this".
Stephanie Kelly, who is representing the family with law firm Slater and Gordon, said: "Selwa's heart condition was serious but it was treatable and she was an otherwise healthy young woman.
"Had she been diagnosed earlier there is no reason she would not have had many more happy years with Muhanad and her daughter.
"Both had endured so much hardship in their young lives already but had finally found happiness and for it to be torn away like this is heartbreaking.
"Sadly Saden will never know her mum but Muhanad is a wonderful dad who is determined to honour Selwa's memory by making sure that lessons are learnt from this."