Opponents swiftly denounced the legislation and said they would challenge it in court.
Arkansas lawmakers said the law "squares" with other state legislation and the U.S. Supreme Court Roe v. Wade ruling, and should withstand court challenges.
"We have chosen here to utilize language from Roe v. Wade that says the states have an interest in protecting human lives, especially fetuses at approximately the end of the first trimester and the beginning of the second trimester," said state Sen. Jason Rapert, one of the Republican leaders for the Arkansas Human Heartbeat Protection Act.
"That happens to be 12 weeks," he said.
"We believe that because we put it at 12 weeks it will survive a court challenge - we are setting it at the end of the first trimester," said Arkansas Rep. Ann Clemmer, who shepherded the bill in the state House.
Moreover, the act "squares" with a state fetal-homicide law, Mr. Rapert said.
Arkansas law "declares a 12-week-old baby in utero to be a person and we have prosecuted individuals who have hurt babies in utero," Ms. Clemmer said.
Because an unborn child is a person at 12 weeks in Arkansas, she added, "let's protect that person. There are two people involved now."
On Monday, Arkansas Gov. Mike Beebe, a Democrat, vetoed the measure, known as Senate Bill 134, saying he did not think it was constitutional and would cost the state money to defend.
The state Senate easily overrode the veto Tuesday, and the House followed suit with a 56-33 vote Wednesday. The record would be corrected to show a 57th House member also voted for the measure, Ms. Clemmer said.
The law goes into effect 90 days after lawmakers adjourn in May.
The "heartbeat" law requires women seeking abortions at 12 weeks or later to receive abdominal ultrasounds. If a fetal heartbeat is detected, the abortion is not permitted in most cases. Exemptions include pregnancies that result from incest or rape, or in cases of "medical emergency" in which the woman's life is in danger or the fetus has a "highly lethal" disorder.
These exceptions are what made the bill "successful where many other bills have failed," Mr. Rapert said.
Pro-life supporters were pleased with the bill's passage.
"We are very excited for this law," said Vikki Parker, executive director of A Woman's Place Pregnancy Center in Cabot, Ark. "It's going to save a lot of babies" - and "a lot of women."
Pro-choice organizations pledged to challenge the "extreme" law in court.
"We are deeply disappointed that the Arkansas legislature voted to impose the most restrictive ban on safe and legal abortion in the country," said Cecile Richards, president of the Planned Parenthood Action Fund.
Anthony D. Romero, executive director of the American Civil Liberties Union, said the legislature now has "the shameful distinction of passing the worst impediment to women's reproductive health in decades."
State lawmakers have turned their backs on the women of Arkansas, said Rita Sklar, executive director of ACLU of Arkansas. "We will fight this law in court to ensure that politicians cannot deny women the ability to make their own decisions about their own health."
While "heartbeat" bills have been attempted in other states, this is the first one to be enacted.
"I know that the eyes of the nation were on the Arkansas House of Representatives today, and what you see happening is that people are waking up," Mr. Rapert said.
With 53 million abortions since 1973, "we have had a very irrational policy on abortion in our nation. ... I am asking us to have a conscience and to wake up to this issue, and I believe this [law] is a great step in that direction."
A service of YellowBrix, Inc.