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 implanted under the skin, usually on the left side of the chest below the collarbone. The procedure takes about an hour, and most patients go home within a day. Types of pacemakers vary; some correct a slow heartbeat, while others stop an irregular heartbeat or stop severe heart failure.