Marilyn Cawthon has been a nurse for 30 years. "All my life I provided health care to people," she said recently. "I thought when I needed it, it would be there and wouldn't drive me broke or crazy."

It nearly did both.

Cawthon got the heart care she needed, but insurance refused to pay - and she was billed $24,000.

Now an intensive care nurse at Lower Bucks Hospital in Bristol Township, Cawthon, 57, ultimately got her insurer to pay - four years later.

Her experience turned her into a foot soldier in the fight to bring single-payer universal health care to the United States.

She will be handing out literature today when U.S. Rep. John Conyers (D., Mich.), sponsor of H.R. 676, a bill to create a single-payer system, holds a town-hall meeting at 10:30 a.m. at Thomas Jefferson University, 11th and Locust Streets.

Conyers will be at the University of Pennsylvania Newman Center, 3720 Chestnut St., at 1 p.m. for a second town meeting.

"Trying to talk to insurance companies, sending certified letters, calling on the phone, talking to people who said they'd take care of this only to have them never take care of this," Cawthon explained, "I felt like I was in a maze."

"When people are sick," she added, "the last thing they should be worrying about is money. They should be worrying about getting better. The way it is now . . . people are worried about how they are going to pay for it. And that shouldn't be."

Single payer is a dramatic change favored by millions of Americans and thousands of health-care professionals, but not supported by President Obama. He is determined to bring about health-care reform this year, but says the United States isn't ready for that option.

Under a single-payer plan, Americans would contribute to a health-care trust fund through a variety of means, such as a payroll tax, and this fund would pay doctors, hospitals and nursing homes for care. Patients could still choose doctors. There would be no need for insurers.

"The president said, if we were starting from scratch, that would be an excellent way to go," said Melody Barnes, head of Obama's Domestic Policy Council, "but at this point, we have to build on our current employment-based system to move forward."

Obama said Thursday, "I think most of us would agree that if we want to cover all Americans, we can't make the mistake of trying to fix what isn't broken. So if somebody has insurance they like, they should be able to keep that insurance."

Opponents of the single-payer plan say it will result in longer waits to get into hospitals and to see specialists. Since health care will appear to be free, they say, demand will rise, and the government will ration care to control costs, leading to a chronic shortage of physicians.

Cawthon is undaunted. Understanding what she went through might explain why.

Roll back to 2000. Cawthon was a single mother, divorced, supporting two children.

She was suffering from shortness of breath. Her father died of a heart attack at 45, so she knew not to mess around. She went for a stress test in September. Positive.

That day, she quit smoking.

She needed a cardio-catheterization - doctors would go in and check the arteries and valves of her heart, looking for blockages. She scheduled the test for January 2001. She didn't want to have it before then, because her older daughter was expecting a baby.

In December, a month before the procedure, Cawthon left her job in home health with Jefferson, where she had Personal Choice insurance coverage.

In her new job as a contract nurse, she wouldn't have insurance. So she thought about keeping her coverage through Jefferson for 18 months, as allowed by the federal COBRA law. She would just pay the premiums out of pocket, rather than having Jefferson pay.

But on Dec. 18, Cawthon called Blue Cross and asked about an individual plan.

About 170 million Americans get group insurance through their jobs. About 17 million buy insurance through individual plans on the open market.

In Pennsylvania, if a person is healthy, individual plans can be cheaper than paying to continue coverage under a group plan through COBRA.

As a single mother, Cawthon was always looking for ways to economize, she said. She signed up.

She wanted to make sure that if she switched plans, she'd still be covered for her surgery.

A letter from Independence arrived Jan. 2, the day before her procedure.

"The requested service has been approved."

Another paragraph began:

"This letter is not a determination of eligibility or a guarantee of payment."

Did these mean opposite things? She was confused.

She went ahead the next day and the procedure went well. Her doctor found a clogged artery, did angioplasty to unblock it, put in a stent. She is grateful and thinks this prevented a heart attack.

On Jan. 22, three weeks later, Cawthon received a one-page form letter from Temple University Hospital. It read:

"We have been notified by Blue Cross that your claim for benefits has been DENIED. The reason for this denial is: claim was denied for pre-xcondition. This bill, in the amount of $24,471.82, is now your responsibility."

Cawthon lit a cigarette.

Here is what happened:

When an American is covered in a group plan through an employer, the insurer cannot deny coverage because of a preexisting condition.

But when a person seeks an individual plan, in Pennsylvania and 43 other states, coverage can be denied for a preexisting condition.

One trigger allowing an insurer to deny coverage is a lack of insurance in the previous two years.

Before Cawthon worked at Jefferson, she'd gone through February, March and April of 2000 without insurance. That allowed Independence to look at her medical history, see she had a heart ailment, and deny her coverage.

Hence, the $24,000 bill.

The confusing letter she received the day before her procedure confirmed that she needed help, but also said coverage couldn't be guaranteed. Cawthon said she didn't understand.

It gets more complicated.

The law gave Cawthon 63 days after she left Jefferson to get covered under COBRA.

Temple sent Cawthon the bill. But she didn't get an official denial from the insurer for nine months - too late to go back and get the surgery covered under COBRA. She was stuck with a $24,000 bill she said she couldn't pay.

The debt ruined her credit rating. The interest rate of her car loan was 16 percent.

On Nov. 20, 2004, she read a newspaper story about G. Fred DiBona, president and chief executive officer of Independence, and his fight with cancer and determination to live.

Cawthon wrote him that night. She hoped he would beat the cancer. She also told him, "I counted on your insurance company to help me out, and it's been a nightmare."

A letter came back, signed by Fred DiBona. He said he'd look into it. He died soon after. But he had been good to his word.

On Jan 19, 2005, a letter came from the insurer: "A decision has been made to ... have the claim reprocessed for payment. . . . This . . . is a one-time exception."

Marilyn cried that day.

She interprets the letter as: "In honor of Fred, we're going to give you a break."

Elizabeth Williams, an Independence spokeswoman, said that wasn't the reason. The denial "was accurate," Williams said, "but the period between when she had the surgery and October, when she got that letter, that's an unnecessary delay."

All this led Cawthon to support a single-payer plan, she said, to hand out literature today. Every day, she helps save lives. Only now, she often wonders, "Are these patients going to go through the same thing I went through?"

"The whole thing is about quality of life," she said. "You don't want to give patients another heart attack when you start pummeling them with bills."