Having a pet might lower a person's risk of heart disease, but it may be simply that healthier people have pets, U.S. researchers say. An American Heart Association scientific statement published online in the association's journal Circulation said pet ownership is probably associated with a reduction in heart disease risk factors and increased survival among patients. But the studies aren't definitive and do not necessarily prove that owning a pet directly causes a reduction in heart disease risk. Dr. Glenn N. Levine, professor at Baylor College of Medicine in Houston and chairman of the committee that wrote the statement after reviewing previous studies of the influence of pets, said, "It may be simply that healthier people are the ones that have pets, not that having a pet actually leads to or causes reduction in cardiovascular risk." Dog ownership in particular might help reduce cardiovascular risk because people with dogs may engage in more physical activity because they walk them. In a study of more than 5,200 adults, dog owners engaged in more walking and physical activity than non-dog owners and were 54 percent more likely to get the recommended level of physical activity. In addition, owning pets might be associated with lower blood pressure and cholesterol levels, and a lower incidence of obesity. Pets could also have a positive effect on the body's reactions to stress. "In essence, data suggest that there probably is an association between pet ownership and decreased cardiovascular risk," Levine said. "What's less clear is whether the act ofadopting or acquiring a pet could lead to a reduction in cardiovascular risk in those with pre-existing disease. Further research is needed to more definitively answer this question."