In a recent statement, HCA declined to provide evidence that it had alerted Medicare, or state Medicaid, or private insurers of its findings or reimbursed them for any of the procedures the company later deemed unnecessary, as required by law.

HCA said in a statement: “When the company becomes aware of a situation in which we might have a reimbursement obligation, we assess, with outside resources, what our reimbursement obligations might be.”

HCA also declined to show that it had ever notified patients, who might have been entitled to compensation from the hospital for any harm.

Some doctors accused in the reviews of performing unnecessary procedures are still practicing at HCA hospitals.

The cardiologists say the reviews of their work did not accurately reflect the care they provided, and HCA says the reviews “are not, by any means, definitive,” according to an emailed response by the company. HCA says it took whatever steps were necessary to improve patient care. It also said “significant actions were taken to investigate areas of concern, to bring in independent reviewers, and to take action where necessary.”

Details about the procedures and the company's knowledge of them are contained in thousands of pages of confidential memos, email correspondence among executives, transcripts from hearings and reports from outside consultants examined by The Times, as well as interviews with doctors and others. A review of those communications reveals that rather than asking whether patients had been harmed or whether regulators needed to be contacted, hospital officials asked for information on how the physicians' activities affected the hospitals' bottom line.

HCA denies its decisions at these hospitals were motivated by financial considerations, but rather “demonstrate the strong focus we have on quality patient care.” The company also says that more than 80 percent of its hospitals are in the top 10 percent of government rankings for quality.

Although HCA has hospitals in about 20 states from California to Virginia and Alaska to Texas, Florida, with its large older population, is a critical and growing market for hospital chains and especially for HCA. HCA's Florida hospitals provide about 20 percent of the company's revenue.

The need to root out Medicare fraud — billing for unnecessary procedures, for example — is high for all hospitals. In 2003, Tenet Healthcare agreed to pay $54 million to settle allegations that unnecessary cardiac procedures were being performed over six years and billed to Medicare and Medicaid at one of its hospitals in California, Redding Medical Center.

But the pressure is even greater for HCA. In 2000, the company reached one of a series of settlements involving a huge Medicare fraud case with the Justice Department that would eventually come to $1.7 billion in fines and repayments. The accusations, which primarily involved overbilling, occurred when Rick Scott, now the governor of Florida, was the company's chief executive. He was removed from the post by the board and was never personally accused of wrongdoing.

As part of the settlement with the federal regulators, HCA signed a 97-page Corporate Integrity Agreement that extended through late 2008. It detailed what had to be reported to authorities and provided for stiffer penalties if HCA failed to do so.