The Mariana Islands are shown, with the territory of Guam to the extreme south, and the Commonwealth of the Northern Mariana Islands (14 islands) to the north. Active volcanoes are shown with triangles. The Mariana Islands (also the Marianas) are a crescent-shaped archipelago comprising the summits of fifteen mostly dormant volcanic mountains in the western North Pacific Ocean, between the 12th and 21st parallels north and along the 145th meridian east.
People with congestive heart failure are often given pacemakers to help their hearts pump more efficiently. But doctors have been puzzled by about 40 percent of people given those devices who don't get any better. They often wind up in the hospital, or they die. Now researchers say they've got the problem figured out.
A pacemaker is a small electrical device which is used to treat some abnormal heart rhythms that can cause your heart to beat too slowly or miss beats. Some pacemakers can also help the chambers of your heart beat in time.