A small study showed that visits from therapeutic dogs lowered anxiety, stress and heart and lung pressure among heart failure patients.
"I'm not surprised at all that something that makes people feel good also makes them feel less anxious, has measurable physiological effects," said Marc Gillinov, a cardiac surgeon at the Cleveland Clinic who was not involved in the study.
"You can see it on their face, first you see a smile and then you see the worries of the world roll off their shoulders," said Kathie Cole, a nurse at the University of California Los Angeles Medical Centre who led the study presented on Tuesday at an American Heart Association meeting.
Take Charles Denson, for example. His face brightened as a speckled Australian Shepherd named Bart cuddled next to him as he rested in his hospital bed in a cardiac care unit.
"You've got a pretty coat," the 51-year-old said, while petting Bart's soft fur.
Cole and her colleagues studied 76 heart failure patients - average age 57 - who got either a visit from a volunteer, a volunteer plus a dog, or no visit.
The scientists meticulously measured patients' physiological responses before, during and after the visits.
Anxiety as measured by a standard rating scale dropped 24% for those visited by the dog and volunteer team, but only by 10% for those visited by just a volunteer. The scores for the group with no visit remained the same.
Levels of epinephrine, a hormone the body makes when under stress, dropped about 17% in patients visited by a person and a dog, and 2% in those visited just by a person. But levels rose about 7% in the unvisited group.
Heart pressure dropped 10% after the visit by the volunteer and dog. It increased 3% for those visited by a volunteer and 5% for those who got no visit. Lung pressure declined 5% for those visited by a dog and a volunteer. It rose in the other two groups.
"I'm not surprised at all that something that makes people feel good also makes them feel less anxious, has measurable physiological effects"
Gillinov said the study was especially impressive because of the hard data it provided as opposed to observations.
Cole has said that she hopes the study, funded by the Pet Care Trust Foundation, a non-profit organisation that promotes the value of animals in society, will help to show that pet therapy is a credible addition to patient care, not just a nicety.
"It makes the hospital seem less like a hospital and it lowers people's blood pressure," said Linda Marler, education coordinator for Baylor Institute for Rehabilitation and animal assisted therapy coordinator for Baylor Healthcare System.
The dogs used in the study - which ranged from a poodle to a golden retriever to a miniature schnauzer - were carefully screened at UCLA and had to pass a behaviour test and checkup by a veterinarian, Cole said. Patients were also asked if they liked dogs and wanted to be part of the study.
Dr George Dennish, a cardiologist at Scripps Memorial Hospital in La Jolla, California, said that he occasionally used dogs in therapy.
"(The patients) felt better, they felt calmer, they felt more satisfied," Dennish said.
But he said more long-term studies with more people needed to be done.