The fish-oil studies tested prescription-strength omega-3 capsules from several companies in two different groups of people for preventing atrial fibrillation, a fluttering, irregular heartbeat.
One study from South America aimed to prevent recurrent episodes in 600 participants who already had the condition. The other sought to prevent it from developing in 1,500 people from the U.S., Italy and Argentina having various types of heart surgery, such as valve replacement. About one third of heart-surgery patients develop atrial fibrillation as a complication.
Both studies found fish oil ineffective.
AP Medical Writer Lindsey Tanner in Chicago contributed to this report.
Vitamin facts: http://ods.od.nih.gov/factsheets/MVMS-QuickFacts/
Dietary advice: www.dietaryguidelines.gov
Marilynn Marchione can be followed at http://twitter.com/MMarchioneAP.