NEW YORK (CNN/Money) - A medical trial showing the benefits of implantable defibrillators for patients suffering from heart failure boosted shares of cardiovascular device makers Medtronic and Guidant Monday.

Approximately five million Americans suffer from heart failure, a progressive condition that causes the lower chambers of the heart to lose their ability to pump blood. Implantable defibrillators (ICDs), the trial showed, lowered the risk of sudden cardiac arrest in patients with moderate heart failure by 23 percent.

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"These findings should have a big impact on the treatment of heart failure patients," Dr. Barbara Alving, acting director for the National Heart, Lung, and Blood Institute (NHLBI), said in a statement. The NHLBI is a division of the National Institutes of Health.

"Until now, it was not known if implanted defibrillators would help such a wide range of heart failure patients, including those whose heart failure may not have been caused by a heart attack," she added.

At least one analysts says the news could expand the $3.8 billion market for heart device makers.

"The population of patients that can benefit from ICDs has expanded by almost twofold," Piper Jaffray analyst Thomas Gunderson told Reuters.

Gunderson said a Piper Jaffray survey of doctors before the results were released indicated that positive trial results would increase the number of patients they refer for ICD therapy by 20 percent in the first 12 months.

Medtronic (MDT: up $1.59 to $50.14, Research, Estimates) shares jumped nearly 3 percent in afternoon trading following the news while Guidant (GDT: up $1.47 to $72.97, Research, Estimates) shares advanced by more than 2 percent. Rival St. Jude Medical (STJ: up $1.02 to $77.52, Research, Estimates) moved 1 percent higher on the news.  

--from staff and wire reports