Amodia Teresita Palacio was arrested for possession of more than five kilograms (11 pounds) of the drug in April at a Hanoi airport, the clerk told AFP.
She was found guilty of repeatedly entering the country from Thailand to smuggle drugs, the clerk said following Tuesday’s trial.
A spokesman for the Philippine Department of Foreign Affairs in Manila confirmed the death sentence, adding that Palacio has 15 days to appeal.
“We will exhaust all avenues of appeal to save her life,” said Raul Hernandez.
Communist Vietnam’s drug laws are among the toughest in the world and anyone found guilty of possessing more than around half a kilogramme of heroin faces the death penalty.
In June, Vietnam sentenced a 23-year-old Thai design student to death for trafficking three kilogrammes of amphetamines.
At present, there are more than 400 prisoners on death row in the country, mostly for cases involving drugs or murder, but executions have declined in recent years.
Since July 2011, when Vietnam replaced execution by firing squads with lethal injections, no prisoners have been put to death as the country failed to import the lethal drugs needed to carry out the penalty.
Forty-three people have received death sentences since the start of this year, mainly for murder and drug charges.