"The Joint Commission is aware of patient safety-related events at St. Mary's Medical Center," according to a statement by the commission. "The Joint Commission takes patient safety and quality concerns very seriously."
Evaluations from the Joint Commission are significant, said Dr. Keith Oldham, the medical director of the children's surgery verification program at the American College of Surgeons.
"The Joint Commission brings external scrutiny to hospitals, and external scrutiny is very important," he said.
Earlier this month, the federal Centers for Medicare and Medicaid Services announced it would be launching an investigation into the program.
A spokeswoman for St. Mary's did not respond to emails seeking comment on the two investigations into the hospital's pediatric surgery program. In a statement to CNN earlier this year, St. Mary's CEO Davide Carbone said his hospital is "continuously taking steps to improve our program and operate it with the highest possible standards of excellence."
For its story, CNN interviewed parents of nine babies who passed away between 2011 and 2015 after having heart surgery at St. Mary's, and the parents of another baby, Layla McCarthy, whose legs were left paralyzed.
"I think this is wonderful," Layla's mother, Christine McCarthy, said about the Joint Commission's evaluation. "I'm glad people are taking a deeper look at things and taking this seriously."
Dr. Ana Pujols McKee, the chief medical officer for the Joint Commission, said her group receives more than 20,000 complaints a year about hospitals and other health care institutions. She declined to give specifics about her group's evaluation of the children's heart surgery program at St. Mary's.
"Part of what makes our evaluation effective is its unannounced nature," she said. "We guard that quite highly. We count on walking into an organization without any preparation on the part of the organization."
She said in general, the commission interviews patients, families, and hospital staff members, examines patient records, and tries to make sure the hospital has followed safety processes and procedures.
"When the complaint is that there's been risk or harm to patients, we'll send out a special surveyor," she said. "We substantiate about 67% of the complaints through this process. That's a very high substantiation rate."
In its investigation, CNN calculated that from 2011-2013, the raw mortality rate at St. Mary's for pediatric open heart surgeries was 12.5%, which is more than three times higher than the national average for such surgeries during that time. After the story aired, St. Mary's released a statement
saying CNN's number was "wrong," "exaggerated," and "completely erroneous."
St. Mary's says its congenital heart surgery program had a 5.3% mortality rate, risk-adjusted, for the four-year period ending on June 30, 2014. It sourced its figure to the Society of Thoracic Surgeons, noting the hospital performed its "first STS reportable" congenital heart surgery in September 2011. It's impossible to independently verify that, because the society won't release data about individual hospitals, and St. Mary's refuses to make public its report from the society or otherwise provide data to explain or support how its figure was calculated.
The hospital claims there "is no statistically significant difference in our program's mortality rate from the national average." The STS national average for congenital heart surgery mortality was 3.4% for the four-year period ending on June 30, 2014.
The hospital has also not made public either raw or risk-adjusted data specifically for pediatric open heart surgeries for the period CNN evaluated. CNN based its calculation on records the hospital filed with the state regarding such surgeries.
It's not clear whether the commission will try to access either St. Mary's report from the Society of Thoracic Surgeons or another potentially important document -- a confidential peer review of the program performed last year by Dr. Jeffrey Jacobs, a professor of cardiac surgery at Johns Hopkins University.
"If I were evaluating this program, I'd want to see these," said Oldham, the surgeon in chief at Children's Hospital of Wisconsin. "I would want to see what an outside expert had to say."
The Joint Commission does have access to an expert review sponsored by the state of Florida.
Jacobs headed that review, and said St. Mary's was doing too few pediatric heart surgeries "to acquire and maintain proficiency in these types of challenging procedures."
The situation, he wrote, "is not the failure of any one individual. It is the failure of the entire team and system."
Jacobs recommended last year that St. Mary's stop doing heart surgeries on babies younger than 6 months old and no complex heart surgeries on any child. The hospital did not follow this recommendation, and this year two babies, each just a few weeks old, died after having heart surgery at St. Mary's.
After CNN's reporting earlier this month, the hospital "launched a comprehensive review of the pediatric cardiac surgery program." The hospital said it did not intend to schedule any further elective surgeries until its review is completed.
Speaking about hospitals in general and not St. Mary's in particular, Dr. Tejal Ghandi, the president and CEO of the National Patient Safety Foundation, said evaluators should find out whether a hospital's culture - encourages or discourages staff members to voice safety concerns.
"Is that junior nurse who just arrived able to question the surgeon and not get reprimanded for it, but actually thanked?" said Gandhi, an associate professor of medicine at Harvard Medical School.
In a statement to CNN earlier this year, Carbone said St. Mary's has "worked diligently to attract and retain clinical staff with expertise in pediatric cardiovascular surgery, including not only physicians but also nurses and Pediatric Intensive Care Unit intensivists."
Speaking in general and not about St. Mary's in particular, Dr. Charles Fraser, the chief of congenital heart surgery at Texas Children's Hospital in Houston, said if he were evaluating a pediatric heart surgery program, he'd want to know specifically how many staff members were specially trained to take care of pediatric heart surgery patients.
"I've seen this happen time and time again where a hospital says they're going to start a pediatric heart surgery program and then they realize it's very expensive," he said, "They really need to stay the course and keep investing in all the things that are necessary to keep the patient surrounded by the greatest expertise at all times, and that includes cardiac-trained intensive care nursing, which is critical," he added.
Fraser's pediatric heart surgery program is ranked No. 2 in the nation by US News & World Report.
"If a hospital isn't willing to commit to that, you start to be concerned. I start to be concerned," he said.