It is impossible even for surgeons to see the inside of the beating heart in detail with the naked eye. Japanese doctors, mechanical engineers and mathematicians cooperated to develop the heart simulator to reproduce each patient's heart. The simulator analyzes the movements of the heart's molecules, numbering 1 billion x 1 billion, to visualize the heart in 3D. It can also predict postoperative conditions. Clinical trials started in 2022 to save the lives of infants who have heart defects.