Your heart is a miracle in motion, a marvel of construction unsurpassed by any human-made creation. It beats 100,000 times every day—if you were to live to 100, that would be more than 3 billion beats across your lifespan. Despite decades of effort in labs all over the world, we have not yet been able to replicate the heart’s perfect engineering. But, as Sian Harding shows us in , new scientific developments are opening up the mysteries of the heart. And this explosion of new science—ultrafast imaging, gene editing, stem cells, artificial intelligence, and advanced sub-light microscopy—has crucial, real-world consequences for health and well-being. Harding—a world leader in cardiac research—explores the relation between the emotions and heart function, reporting that the heart not only responds to our emotions, it creates them as well. The condition known as Broken Heart Syndrome, for example, is a real disorder than can follow bereavement or stress. describes the evolutionary forces that have shaped the heart’s response to damage, the astonishing rejuvenating power of stem cells, how we can avoid heart disease, and why it can be so hard to repair a damaged heart. It tells the stories of patients who have had the devastating experiences of a heart attack, chaotic heart rhythms, or stress-induced acute heart failure. And it describes how cutting-edge technologies are enabling experiments and clinical trials that will lead us to new solutions to the worldwide scourge of heart disease.