Almost 1,000 Americans die each day from cardiac arrest, according to the American Heart Association. Cardiopulmonary resuscitation is a critical life-saving technique, but nationwide it saves less than 10 percent of victims.
The problem is, studies show, even emergency medical teams often perform CPR improperly. Now some cities have turned to a portable machine to do the job.
Manual chest compressions usually restore only about 40 percent of blood flow to the brain and about 20 percent of blood flow to the heart, meaning that even those who are saved are often left with brain damage.
"We're probably not compressing hard enough," said Dr. Paul Pepe, chair of Emergency Medicine at the University of Texas Southwestern Medical Center. "We're probably not compressing fast enough, and we're probably interrupting to give breaths too often to be effective, or as effective as we could be."
The solution, say some paramedics, is a new portable chest compressor.
Once the victim has been strapped in, the machine calculates the person's shape and size to deliver the optimal chest compression -- just the right pressure and frequency for that particular patient.
Unlike manual CPR, the machine can compress the chest without stopping.
"I feel very passionate about this machine and believe that it not only saved my life but allowed me to have a complete recovery," said Caralee Weich, a cardiac arrest survivor.
Weich went into cardiac arrest on a San Francisco sidewalk last year. She had no pulse for 30 minutes, but she was hooked up to an automated chest compressor.
"It kept me going," said Weich. "It kept the blood flow going. It allowed the medication they gave me to circulate better through my system."
One of the several models approved by the Food and Drug Administration sells for $15,000. About 100 U.S. cities and towns now have at least one.
Preliminary studies suggest that patients who got automated chest compression were 35 percent more likely to arrive at emergency rooms with a beating heart, than those given traditional manual CPR.
The American Heart Association wants to see more studies to ensure the machines not only increase blood flow, but that they actually allow more patients a full recovery.
ABC News' John McKenzie filed this report for "World News Tonight.