The woman was 31 weeks pregnant when she visited the emergency room at St Göran Hospital in Stockholm in January this year.
Doctors took an ECG, and examined her heart and lungs, and found that she had an enlarged aorta. However, they did not consider her condition to be acute, writes Swedish public radio P4.
Her pain was thought to be muscle or skeleton-related, and she was sent home with an Alvedon – a Swedish paracetamol brand – and a referral for an ultrasound of her heart ahead of the due date.
But only around 14 hours later she came back with cardiac arrest, and died in hospital.
The hospital has reported itself to Sweden's medical watchdog.
“It is a deeply tragic incident,” St Göran chief physician Måns Belfrage told P4.