U.S. District Judge Susan Webber Wright last year had stopped enforcement of the law while she reviewed it, and on Friday she declared that it was unconstitutional. She cited previous court decisions that said abortions shouldn't be restricted until after a fetus reaches viability, or when a fetus could be expected to survive outside the womb. That is typically at 22 to 24 weeks.
"The state presents no evidence that a fetus can live outside the mother's womb at twelve weeks," the judge wrote.
By adopting a ban based on a fetal heartbeat, and not the ability to survive, the Arkansas Legislature had adopted the nation's toughest abortion law last March. Two weeks later, North Dakota lawmakers passed a bill restricting abortions at six weeks - or before some women would know they're pregnant. That law is on hold.
In her decision Friday, Wright said only a doctor could determine viability.
"The Supreme Court has ... stressed that it is not the proper function of the legislature or the courts to place viability at a specific point in the gestation period," Wright wrote.
Wright left in place a portion of the law that requires doctors to check for a fetal heartbeat and to notify the pregnant woman if one is present.
Bettina Brownstein, who represented two doctors who perform abortions at a Little Rock clinic, said the 12-week ban was "demeaning to women."
"The law never should have been passed in the first place, it's so unquestionably unconstitutional," she said. She said it was unlikely that Drs. Louis Jerry Edwards and Tom Tvedten would appeal the portion of the law requiring them to notify patients if a heartbeat is detected.
"Practically, in my opinion, it has very little effect. It's duplicative of what doctors who perform abortions in Arkansas already have to do," she said.
State Sen. Jason Rapert, R-Conway, who sponsored the fetal heartbeat bill, said he was encouraged that that portion of the measure was upheld.
"Now, anyone who presents for abortion in our state, they're going to be given an opportunity to know if there's a living heartbeat in their womb, and that is a win for the pro-life movement," Rapert said. "When people have to face the reality that there's a living heartbeat in their womb, that will make them rethink about taking the life away from their baby."
The 12-week ban had included exemptions for rape, incest, the life of the mother and highly lethal fetal disorders.