During cardiac arrest time is of the essence, but a longer period of cardiopulmonary resuscitation may be no better than a shorter one, a study finds. The study, released Wednesday in the New England Journal of Medicine, compared outcomes of 9,933 cardiac arrest patients, about half of whom had 30 to 60 seconds of initial CPR from paramedics, or three minutes of the procedure, before heart rhythms were analyzed. In both groups, 5.9% of patients survived and were discharged from the hospital in acceptable health. Resuscitation guidelines released in 2005 from the American Heart Assn.-International Liaison Committee on Resuscitation recommended that emergency responders do CPR for two minutes before evaluating heart beats. In 2010 the guidelines became less stringent, acknowledging that evidence didn't necessarily support doing CPR for a longer amount of time. The study also found that patients who received CPR from a bystander may do better if they then had shorter CPR from a paramedic. "Our study definitely shows that there is a no advantage to a longer period of initial CPR," said Dr. Ian Stiell, the study's lead author, in a news release. Although the study didn't evaluate people who didn't receive any CPR before having their cardiac rhythms analyzed, the authors wrote it's still essential to give CPR for some time while defibrillator pads are being readied.