As the right to an abortion protected by Roe v. Wade appears increasingly likely to be overturned by the U.S. Supreme Court, all eyes in Pennsylvania are on Harrisburg to determine what abortion access could look like in the future.

Legislation that has significant momentum among Pennsylvania Republicans and in a handful of other states is what proponents dub “heartbeat bills.” Such legislation — which in Texas triggered a near-total ban on abortion — prohibits the procedure after ultrasound screening picks up an embryo’s cardiac activity, which can happen as early as six weeks into a pregnancy and before many are aware they’re pregnant.

This activity is not yet a true heartbeat, as there are no valves opening and closing to create an audible lub-dup sound. What you hear in the doctor’s office at six weeks is artificially generated by the ultrasound machine, as we’ll explain below.

Here’s what the legislation would do, and why it’s seen as one of the greatest threats to abortion access in Pennsylvania:

What would a ‘heartbeat’ bill do if it became law?

Current Pennsylvania law allows for abortions to be performed at any point up to 24 weeks from the pregnant person’s last menstrual period. The procedure can be done later in a pregnancy in some cases of medical emergencies.

Pennsylvania does not have what’s known as a “trigger law,” meaning that the overturning of Roe would not immediately change abortion laws in the state. In order for it to be further restricted, both chambers of the General Assembly would have to pass legislation that the governor then signs.

» READ MORE: How the Mississippi Supreme Court case could affected Pa. law

Several committees have considered the six-week ban on abortion, but it hasn’t before reached the governor’s desk.

Sen. Doug Mastriano (R., Franklin), a Republican front-runner for governor, is the prime sponsor of similar legislation currently sitting in the Pennsylvania Senate Health and Human Services Committee. He has described limiting access to abortion as his raison d’être and his No. 1 issue.

“I’m going to fight this until my dying breath,” he said in 2019 when he introduced a Senate version of the bill.

A House version of that bill was passed by the Health Committee last year, but it was tabled before a full vote.

When the heartbeat really starts

Six weeks into pregnancy, a tube-like loop of cells starts to pulse with the flow of blood. But there are no chambers, and no valves, and therefore no audible beat, said Nisha Verma, a fellow at the American College of Obstetricians and Gynecologists.

“What people think of as a heartbeat in early pregnancy is actually created by electric impulses that are captured by an ultrasound machine and translated by the machine into the sound of a heartbeat,” she said in an email. “There are no cardiac valves, so there is no sound of them opening and closing.”

Using a stethoscope, the physician typically cannot hear a true heartbeat until 18 to 20 weeks into the pregnancy.

Verma acknowledged that many physicians use the term heartbeat at six weeks, because it is relatable for families.

“But that doesn’t mean that it’s clinically accurate or that it should be used to restrict my patients’ access to medical care,” she said.

The role of the governor in legislation

Gov. Tom Wolf, a Democrat, has vetoed antiabortion legislation and has vowed to continue to do so, but he is term-limited and leaves office in January. The Pennsylvania primary for his replacement is May 17.

Democrat Josh Shapiro is the presumptive nominee on the Democratic side, and he has similarly pledged to veto abortion restrictions passed by the legislature, which is currently controlled by Republicans.

» READ MORE: Where the candidates for Pennsylvania governor stand on abortions

On the Republican side, all the candidates running for governor have said they support further restrictions to abortion access, and several polling near the top of the field have suggested they’d sign a six-week ban if it came to their desk.

During a recent debate, Mastriano said he would “move with alacrity” to enact his bill, saying he wouldn’t allow any exceptions for rape, incest, or the life of the mother. He seemed to suggest that a six-week ban would be a first step toward total abortion prohibition, saying, “I’m at conception, we’re gonna have to work our way toward that.”

Former Congressman Lou Barletta in 2017 cosponsored federal legislation that criminalized performing an abortion after cardiac activity is detected.

The leading candidates generally agree that the legislation should carry criminal penalties for physicians who break the law, though none favor prosecuting patients for undergoing illegal abortions.

The makeup of the state legislature is also critical. The General Assembly would likely struggle to pass a six- or eight-week abortion ban if Republicans lost control of one or both chambers.

Where did ‘heartbeat’ bills start?

The first “heartbeat” bill in the country was introduced in Ohio in 2011 and was developed by Janet Porter, an antiabortion activist and founder of the group Faith2Action. Today, the organization offers model legislation to lawmakers across the United States seeking to prohibit abortions as early as six weeks into a pregnancy.

Since then, 14 states from North Dakota to Georgia have passed six-week bans, and most carry criminal penalties for physicians who violate them. The majority of those states passed the legislation in the last three years.

But the laws have faced legal challenges, and the only place where one has taken effect is Texas. Last year, after the U.S. Supreme Court denied a request for emergency relief filed by abortion providers, private citizens became empowered under the law to sue anyone who “aids or abets” an abortion after about six weeks.

What other abortion restrictions have backing in Harrisburg?

Both Republican-controlled chambers in Harrisburg have passed legislation aimed at further restricting access to abortions, and several bills advanced to Wolf’s desk over his two terms.

In 2017, he vetoed a bill that would have prohibited abortion after 20 weeks, about four weeks earlier than current law. The legislation would have also criminalized an uncommon procedure called “dilation and evacuation,” which is a process by which doctors use forceps to remove a fetus.

That bill passed the Senate, 32-18, and the vote in the House was 121-70. The votes were largely along party lines.

In 2019, he vetoed a bill that would have made it illegal for doctors to perform abortions based on a prenatal diagnosis of Down syndrome. The legislation, which had been passed by the House before but died before getting to Wolf’s desk, required physicians affirm an abortion wasn’t performed due to a Down syndrome diagnosis. Doctors who violated the law would face felony criminal charges.

House Republicans advanced a similar bill again last summer.

And earlier this year, the Senate Health and Human Services Committee passed legislation along party lines that would amend the state constitution to say explicitly that there is no constitutional right to an abortion. The bill was tabled last month.