VATICAN CITY – Pope John Paul II (search) was in "very serious" condition after suffering heart failure, the Vatican said Friday morning.
The latest downturn in the pontiff's health developed after he contracted a very high fever brought on by a urinary tract infection on Thursday. He received the Roman Catholic sacrament for the gravely ill and the dying once known as "Last Rites."
Vatican spokesman Joaquin Navarro-Valls said in a statement that the pope experienced septic shock (search) and heart failure on Thursday afternoon. The pope's heart had stopped during treatment for the infection, the statement said.
Heart failure occurs when the organ lacks the strength to pump blood through the body, and indicates that the body's cardiac system is collapsing.
The Vatican's statement, however, also added that "the Holy Father is conscious, lucid, and serene" and had taken part in 6 a.m. mass Friday.
The pope was not rushed to the hospital because he wanted to remain in his apartment, where he was treated by the Vatican medical team and provided with "all the appropriate therapeutic provisions and cardio-respiratory assistance," the Vatican said.
The pope was being helped by a fleet of caregivers: his personal doctor, two intensive care doctors, a cardiologist, an ear, nose and throat specialist, and two nurses.
In Washington on Thursday, Cardinal Theodore McCarrick (search), archbishop of the District of Columbia, called a press conference on Thursday and asked for prayer for the pontiff.
"Pray for the holy father, that he may recover and be able to communicate," McCarrick said. "If this is not the Lord's will, may he not suffer. He's going through a period of suffering. We worry about him."
At the edge of St. Peter's Square, hundreds of people gathered early Friday. A few got down on their knees to pray for the pontiff. Others, having kept vigil through the night, sat cloaked in blankets.
"There's nothing we can do but pray. We're all upset," said Agriculture Minister Giovanni Alemanno, who was in the crowd.
"I was in the car and I heard on the radio about the grave condition of the pope. I immediately thought I would come to St. Peter's," said Antonio Ceresa, a Roman.
The "Last Rites" ritual is the Roman Catholic sacrament reserved for both the gravely sick and the dying and involves anointing the ailing person with special oils.
Currently known as the "Sacrament of the Infirm" since it is also now done for the gravely ill, it used to be known as "Last Rites" or "Extreme Unction" because it was reserved only for the dying in the past.
The sacrament is often misunderstood as signaling imminent death. But it is performed not only for patients at the point of death, but also those facing grave illness or a serious operation — and it may be repeated.
The Rome daily La Repubblica reported Friday that the sacrament was administered by John Paul's closest aide, Polish Archbishop Stanislaw Dziwisz, who serves as his private secretary. Dziwisz had given the pontiff the same sacrament on Feb. 24 just before the pope underwent a tracheotomy to insert a tube in his throat at Gemelli Polyclinic, the newspaper said.
According to its account, John Paul had attended Mass Thursday morning in his private chapel, then did paperwork from an armchair. Abruptly, at 6:45 p.m., John Paul turned ghostly pale and his blood pressure plummeted, the newspaper said.
After antibiotics were administered, the Italian news agency Apcom reported without citing any sources, John Paul's condition was "stable." ANSA, another Italian news agency, said the pope "seems to showing a first positive reaction" to antibiotic therapy.
A urinary infection can produce fever and a drop in blood pressure, said Dr. Marc Siegel, a specialist in internal medicine at the New York University Medical Center.
The pope's risk of such an infection is heightened because he is elderly — which suggests his prostate is probably enlarged — debilitated and run down from the illness that recently sent him to the hospital, Siegel said.
Urinary infections tend to respond well to antibiotics, given either as pills or intravenously, Siegel said.
Hospitalized twice last month following two breathing crises and with a tube placed in his throat to help him breathe, John Paul has become a picture of suffering. When he appeared at his apartment window Wednesday to bless pilgrims in St. Peter's Square, he managed to utter only a rasp.
Later that day, the Vatican announced he had been fitted with a feeding tube in his nose to help boost his nutritional intake.
The use of the feeding tube illustrates a key point of Roman Catholic policy John Paul has proclaimed: It is morally necessary to give patients food and water, no matter their condition.
As Parkinson's disease (search) and other ailments have left him increasingly frail, the pope has been emphasizing that the chronically ill, "prisoners of their condition ... retain their human dignity in all its fullness."
The Vatican's attitude to the chronically ill has been apparent in its bitter condemnation of a judge's order two weeks ago to remove a feeding tube from Terri Schiavo, the severely brain-damaged American woman who died Thursday.
Vatican Cardinal Jose Saraiva Martins, reacting to Schiavo's death, denounced the removal of her feeding tube as "an attack against God."
While John Paul is fully alert, some see parallels in the two cases.
Under John Paul, Vatican teaching on the final stages of life includes a firm rejection of euthanasia, insistence on treatments that help people bear ailments with dignity and encouragement of research to enhance and prolong life.
A 1980 Vatican document makes the distinction between "proportionate" and "disproportionate" means of prolonging life. While it gives room for refusal of some forms of aggressive medical intervention for terminally ill patients, it insists that "normal care" must not be interrupted.
John Paul set down exactly what that meant in a speech last year to an international conference on treatments for patients in a so-called persistent vegetative state.
"I should like particularly to underline how the administration of water and food, even when provided by artificial means, always represents a natural means of preserving life, not a medical act. Its use, furthermore, should be considered, in principle, ordinary and proportionate, and as such morally obligatory."
John Paul's 26-year papacy has been marked by its call to value the aged and to respect the sick, subjects the pope has turned to as he battles Parkinson's disease and crippling knee and hip ailments.
The Rev. Thomas Williams, a Rome-based theologian, said there are parallels between Schiavo and John Paul, based on the church teaching that such feeding is required. "In that sense, there is a great similarity," he said.
But he pointed out that the pope has been fully conscious and running the church. Court-appointed doctors had determined that Schiavo was in a persistent vegetative state with no hope of recovery before her death. Schiavo's parents had argued that she could get better and that she would never have wanted to be cut off from food and water.
It is not clear who would be empowered to make medical decisions for an unconscious pope. The pope has no close relatives, but the Vatican has officially declined to comment whether John Paul has left written instructions.
FOX News' Greg Palkot, Catherine Donaldson-Evans and The Associated Press contributed to this report.