The gastric microbe, Helicobacter pylori, that's the cause of most stomach ulcers also takes it out on the heart. People with rapid beating of the upper chamber of the heart, atrial fibrillation, are nearly 20 times more likely to be infected with Helicobacter than are healthy "controls," according to a report in the medical journal Heart. While the exact mechanism is unknown, the theory is that it may relate to autoantibodies that develop in some H. pylori-infected patients. These antibodies, which normally attack an acid pump found on gastric cells, may instead attack a similar pump on cardiac cells, ultimately triggering atrial fibrillation. The new findings are based on a study of H. pylori tests in 59 patients with atrial fibrillation and 45 healthy controls. In the overall analysis, 97 percent of atrial fibrillation patients were positive for H. pylori compared with just 5 percent of controls.