Researchers said closer monitoring of women's health was needed
Doctors should be more vigilant about the threat of heart disease during pregnancy, a study suggests.
The number of maternal deaths related to heart disease in England, Wales and Northern Ireland has doubled since 1990 to 2.27 per 100,000.
The Imperial College London team linked the rise to unhealthy lifestyles and urged better diagnosis and management of underlying heart conditions.
But doctors said practices were improving.
They said the country still had one of the best records on maternal deaths.
The researchers analysed data from the government-backed Confidential Enquiry into Maternal and Child Health, which gathers data on all pregnancies.
The 2.27 per 100,000 rate amounts to 48 deaths in the three years from 2003 to 2005, the BJOG journal reported.
The figures suggested heart disease was not becoming more common - the incidence has remained fairly constant at 0.9% for the past few decades - rather that it was becoming more severe or posing more of a risk.
Researchers said this was linked to increases in maternal ages, smoking, lack of exercise and poor diets which had led to rising rates of obesity, diabetes and hypertension.
Two-thirds of the deaths relating to heart disease occurred in women who were either overweight or obese.
The report also said immigrant women were particularly at risk as the two maternal deaths due to rheumatic heart disease occurred in women who had moved from areas where rheumatic fever was endemic.
Overall, care was considered sub-standard in nearly half of the cases of maternal death related to heart disease.
Researchers said doctors could do more by looking for the signs of heart disease early on in pregnancy and managing the condition after diagnosis - many heart disease drugs such as aspirin and beta blockers can be used during pregnancy.
Report author Dr Emily Gelson said: "We must be more aware of this problem, diagnose it and then manage it to help halt the worrying rise in deaths."
But Maggie Blott, of the Royal College of Obstetricians and Gynaecologists, said doctors were already taking steps to improve care as heart disease screening had become routine at the first hospital appointment during pregnancy
"It is something we are all aware of and trying to prevent. But we must remember that the UK has one of the lowest rates of maternal deaths in the world."
A Department of Health spokesman said it was right women should be monitored, but also urged people to take more care of their health.
She said: "Sadly, this study shows the tragic effects that unhealthy lifestyles and diets, obesity and smoking can have on a pregnant mother's life. This re-emphasises the fact that" healthy mums have healthier pregnancies and healthier babies.
"Our advice is that all women should aim to embark on pregnancy as fit and as healthy as possible."