How heart failed
The heart failure suffered by the Pope occurs when the muscles of the heart become ineffective and are unable to pump enough blood and nutrients around the body.
In the Pope's case it is believed the urinary tract infection he is suffering from caused a high fever and a drop in blood pressure. This caused his heart to overwork, enlarging it until it failed and causing blood to congest in his major organs.
Urinary tract infections are usually treated with antibiotics. But doctors today said that the Pope's age made treatment far more complicated.
Dr Harry Fisch, a professor of clinical urology at Columbia University Medical Centre in New York, said such infections in men the Pope's age can be severe. "They are normally not life-threatening, but in the elderly and debilitated, they can be," Dr Fisch said.
