Though atherosclerosis is an artery problem, microscopic denizens of the intestines may play a surprising role in how the disease plays out. A new study suggests that different mixes of intestinal microbes may determine whether people will have heart attacks or strokes brought on by break-away plaque from the arteries. Compared with healthy people, heart disease patients who have had strokes or other complications of atherosclerosis carry fewer microbes that make anti-inflammatory compounds. These patients also have more bacteria that produce inflammation-triggering molecules, researchers report online December 4 in Nature Communications. Inflammation is thought to promote cardiovascular disease.