Put your hand on your chest or your finger on your carotid artery and find your heartbeat. Got it? Now give that rhythm your undivided attention. Your heart thumps some 100,000 times daily, but how often do you give this vital organ its due? Not often enough, according to the latest research. Despite proven prevention and treatment plans, heart disease remains the number-one killer in the U.S. More than one million Americans suffer heart attacks each year, with about half proving fatal. And while heart-attack rates go up sharply after age 45, men 29 to 44 years old—some of them seemingly healthy athletes—still account for about 34,000 cases annually. To help keep your risk low—now and for decades to come—we've gathered expert advice from cardiologists, trainers, and nutritionists on how to best protect this all-important muscle. You just might want to keep your hand where it is while you read on.