It is also one of the most profitable, having built much of its business on critical care centers which specialize in expensive high-risk procedures, such as heart surgery.
But, as Correspondent Ed Bradley first reported in February, Tenet is now facing allegations that it made some of its profits from overbilling, false diagnoses, and - in at least one hospital - major surgery performed on patients who don't need it.
One of Tenet's most profitable hospitals is Redding Medical Center, located in the shadow of Mount Shasta in Redding, Calif., a quiet town surrounded by farmland.
Since 1989, much of that profit has been generated by the hospital's director of cardiology, Dr. Chae Hyun Moon, who has performed more than 30,000 angiograms and ultrasounds - procedures in which a tube is threaded through a patient's heart to look for clogged arteries.
Based on those tests, he has sent thousands of patients for coronary bypass operations. One patient was Jay Bradley, a 35-year-old father of three. Two years ago, Bradley started having chest pains and went to see Moon. The diagnosis was grim.
"He put the monitor in front of my face, showed me a little artery on there and said, 'Well, this is clogged, and this one's the top front of your heart and there's zero chance of survival.'"
Bradley was checked into the hospital right away, and told he could be called into the operating room at any minute. But then, something even more alarming happened.
He says a nurse came in and under her breath said, "Get out!" As Bradley remembers, the nurse continued and said, "I can get fired for saying this, but I don't think you need the surgery."
Bradley says she then took another doctor to the ward, who came in with his head down and told him: "I don't really think you need this. Maybe you should leave here and go to a big city somewhere."
"At this point, I am going crazy here," says Bradley. "Who's right, who's wrong here? I went home."
The next day, he had more chest pains and went across town to Redding's only other hospital, Mercy Medical Center, where he got yet another surprise.
"They called in a cardiologist who looked at my films and my records. He came up and told me that there was nothing wrong with me at all," says Bradley, who discovered that he was the third patient in the week who had come in from Redding Medical Center and had narrowly escaped having bypass surgery.
"We can't find anything wrong with them," Bradley recalled the doctor saying.
After running tests of their own, doctors from Mercy Medical Center finally diagnosed Bradley with just an irritated nerve or muscle. His chest pain soon ended and has never happened since.
But 61-year-old Tom Mitchell wasn't as lucky. Last July, he was at Redding Medical Center, recovering from an emergency appendectomy when a nurse told him that they were going to check his heart. The very next person he saw was Moon, standing at his bedside and telling him he wanted to do an angiogram.
At the time, Mitchell wasn't even having pains in the chest and had never suspected that he might be having a heart problem. But he was soon alarmed by what Moon told him: "He said, 'See that hanging down right there?' He said, 'That's a widow maker.' And he said, 'That could slough off and you would have a heart attack immediately.'"
"He said, 'You are here. So why don't we take care of it,'" says Mitchell, who admits that the pain medication affected his judgment. "I really was in no shape to reason anything through such as bypass surgery. I was really sick."
Within 24 hours, and only three days after his appendectomy, doctors at Redding Medical Center were operating on Mitchell's heart.
But when 60 Minutes presented the same medical records - along with the film Moon took of his heart - to a group of 11 cardiac specialists, all of them agreed that Mitchell shouldn't have had an angiogram, let alone surgery.
Even worse, Mitchell found out later that most coronary bypasses last less than ten years, which means he may have to have a second heart surgery.
"I feel violated. I feel like a gutted trout almost, from the incision that was made down my chest," says Mitchell. "It goes from my Adam's apple to the bottom of my sternum, completely. They cut me in half."
Kim Schlenker, a critical care nurse who lived in Redding until 1999, says she has seen a number of cases like Tom Mitchell's. She remembers working with other cardiologists when they examined Moon's former patients, and recalls doctors saying, "My God, they bypassed normal coronaries!"
"Many complaints were made," says Schlenker. "Letters were written."
At Redding Medical Center, at least one doctor has told federal authorities that he repeatedly warned Tenet's administrators there about doing "heart procedures ... that may not have been medically necessary."
Other cardiologists in Redding have also told authorities they spoke to Tenet's administrators about "unnecessary heart procedures and surgeries" being performed there. And in 1999, doctors at another hospital alerted Redding Medical Center of their "concern ... that Dr. Moon is unsafe," after several nurses, including Schlenker, had complained about him.
"I thought he was a dangerous man and that he doesn't regard the lives of the patients he is working on," Schlenker says she wrote in her letter.
But Tenet's administrators in Redding not only ignored the warnings about Moon, they built their heart center around his practice — making him director of cardiology, featuring him in their ads and flying him to outlying clinics so he could see even more patients.
By 2001, Moon was doing about five times the number of angiograms performed by most cardiologists. He made Tenet millions of dollars a year, billing $20,000 or more for each procedure.
But it wasn't a doctor or a nurse who finally did something about what was going on at Redding Medical Center. It was a priest, Father John Corapi.
Last June, after Moon informed Corapi that he had a fatal heart condition and needed bypass surgery, he went to a lawyer to prepare a will. He went to confession and then he went to another hospital where he had close friends for the surgery.
"The cardiologist said, 'Excuse me, but what are we bypassing? You're bypassing something when you do a bypass surgery,'" recalls Corapi. "He said, 'I don't see anything.'"
After a series of tests showed that his heart was normal, Corapi called a meeting with Tenet's administrators at Redding Medical Center. He asked them to investigate the case and said "there is something that's not quite right." But the hospital refused. Instead, they told Corapi that he was in a life-threatening situation and that they concurred with Moon's recommendations.
Tenet's administrators also assured him that another anonymous cardiologist had also confirmed Moon's opinion. Meanwhile, Corapi consulted seven other cardiac specialists, who agreed his heart was healthy.
He then called the Redding Medical Center one last time. "It just sticks out in my memory," says Corapi. "Hal Chilton, the CEO, said over the phone, 'We like our position. Seek counsel if you like.'"
Father Corapi did more than seek counsel. He called the FBI, who eventually sent more than 40 agents to raid Redding Medical Center, Moon's office and the office of the hospital's director of cardiac surgery. They confiscated thousands of files, including those of at least 167 patients who died after surgery ordered by Moon.
The news of the raid could not have come at a worse time for Tenet Health Systems. All around the country, a number of Tenet hospitals have recently been subjects of federal actions - from patient endangerment in Florida to evidence of illegal kickbacks to physicians in California. Even government officials in Washington, D.C., have recently filed a lawsuit against Tenet, claiming the company has systematically defrauded taxpayers.
The company's executives sent 60 Minutes a letter stating in part: "We expect to demonstrate in the weeks and months ahead that our internal systems and processes work effectively whenever we became aware of anything that fails to meet the law or our own high standards."
Concerning Dr. Moon and Redding's Chief of Cardiac Surgery, who are both under investigation by the FBI and had declined a request from 60 Minutes for an interview, they wrote: "We were as surprised as everyone by this investigation. The two doctors have practiced in the Redding area for decades and their reputation for providing good care, so far as we know, was impeccable until last October."
But for some, who have been in the health care business for years, Tenet's arguments are very hard to believe.
"When they are running ads for this person, when they have documented charges by people who have called his practice to their attention, time and time again, when their own nurses were complaining, when other physicians were complaining, it is pretty hard for somebody to say, 'Gee, I didn't know,'" says Rep. Pete Stark, a 30-year veteran on health care issues.
The California Democrat has followed Tenet since 1994, when the company paid an unprecedented $379 million to settle fraud claims brought by 28 states and the federal government. Tenet also pled guilty to charges of criminal conspiracy and giving illegal kickbacks to physicians.
"You have people who are willing to break the law and have a record of doing that. These guys are the poster children for unethical business practices," says Stark.
But Tenet executives have said that the doctors under investigation had only what they called a "a loose connection" with the hospital's administrators and doctors.
"That seems to me to be an outright lie. They were providing clerical and medical assistance to Dr. Moon at no cost," says Stark.
"They could suspend his privileges and not make him chief of cardiology."
Since 60 Minutes first aired this story in February, Dr. Moon has lost his malpractice insurance and stopped practicing.
In addition, lawsuits have been filed against Tenet, Redding Medical Center, Dr. Moon and several of the hospital's cardiac surgeons. The federal government has also expanded its investigations of Tenet Healthcare Corporation nationwide, and the company's chief executive officer, Jeffrey Barbakow, has resigned.