Hands, not mouths, are more important for bystanders who perform cardiopulmonary resuscitation, the American Heart Association says.

In a scientific update issued yesterday, the association said chest compressions, or "hands-only CPR," save as many sudden cardiac arrest victims as the combination of chest compressions and mouth-to-mouth rescue breathing.

Because people are less willing to do mouth-to-mouth, the update should prompt more people to choose to aid those who collapse from cardiac arrests.

"Don't be afraid to try it," said Dr. Michael Sayre, chairman of the association's Emergency Cardiovascular Care Committee and author of the statement published in Circulation: Journal of the American Heart Association. "We are sure many lives will be saved if the public does hands-only CPR for adult victims of sudden cardiac arrest."

The association said 310,000 adults in the United States die each year from sudden cardiac arrests that occur outside hospital settings. Bystanders who see someone collapse should call 911, then immediately start chest compressions. Without immediate and effective CPR from a bystander, a person's survival chances decrease 7 percent to 10 percent per minute.

"Unfortunately, on average, less than one-third of out-of-hospital cardiac arrest victims receive bystander CPR, which can double or triple a person's chance of surviving a cardiac arrest," the association said.

Quality chest compressions involve 100 deep compressions per minute with full chest recoil and minimal interruptions. Even if a person has no CPR training, hands-only CPR will improve survival odds, said Dr. Sayre, associate professor in Ohio State University's department of emergency medicine.

The statement updates 2005 guidelines, which advised lay rescuers to use hands-only CPR only if unable or unwilling to provide rescue breaths. The update puts hands-only CPR on par with conventional CPR when used on adults who suddenly collapse.

The new recommendation is based on three large 2007 studies that describe outcomes of hundreds of cases of bystanders performing CPR on cardiac arrest victims. None of the studies documented a negative impact on survival when ventilations were omitted from their actions. Hands-only CPR also is easier to remember and results in more chest compressions and fewer interruptions during the wait for emergency response.

But hands-on CPR shouldn't be used on infants or children, or adults who suffer cardiac arrest from respiratory causes such as drug overdoses or near-drowning, or for any unwitnessed cardiac arrests. In those cases, victims benefit most from chest compressions and rescue breaths, it says.

"With these recommendations, we're more comfortable that compressions offer as much benefit as chest compressions and mouth-to-mouth," said Dr. Fred Harchelroad, chairman of Allegheny General Hospital's department of emergency medicine. "Hopefully, we'll see more people recovering with a beating heart."

In his department about 20 percent of sudden cardiac arrest victims are revived at least for a while, with about 10 percent eventually able to leave the hospital. Most, if not all, survivors underwent CPR soon after collapse, he said.

Paramedics and firefighters say a bystander might be unwilling to deliver mouth-to-mouth ventilation because of concern about disease transmission, while others are reluctant to put their mouths on someone who smells badly or has vomited, as cardiac arrest patients sometimes do involuntarily.

"The mouth-to-mouth would be the largest impediment to helping," said Chief Robert Cox, who is in charge of training for the Pittsburgh Fire Bureau. He said that it's rare to find bystanders performing CPR on cardiac arrest patients when he has arrived on a scene.

Tony Weinmann, president-elect of the Pittsburgh Fraternal Order of Professional Paramedics, speculated that some people become overwhelmed by the complexity of delivering CPR in emergency situations, and that streamlining the guidelines might increase bystander participation.

Dr. Robert Hickey, an emergency department physician at Children's Hospital in Pittsburgh and a former chairman of the association's committee, which published the statement, said: "The important thing to realize is, right now in Pittsburgh and surrounding area, if you fall over with a sudden cardiac arrest, the chance of getting CPR is just one in three."

Mouth-to-mouth ventilation is important in saving near-drowning victims or those suffering respiratory despair.

But in most cases of collapse, the cause is cardiac arrest, Dr. Hickey said.

"This makes it as simple as possible, and people should recognize that you can't hurt someone who is dead," he said.

Instead, the goal is to give that person a chance at survival.

"It all starts with the bystander -- with the person getting on hands and knees and doing CPR," he said. He added that deciding to do CPR can be frightening, "but doing nothing is even more frightening."