Scientists have created a detailed cellular and molecular map of the healthy human heart to understand how this vital organ functions and to shed light on what goes awry in cardiovascular disease. The work, published in the journal Nature, was led by investigators at Harvard Medical School, Brigham and Women's Hospital, the Wellcome Sanger Institute, Max Delbruck Center for Molecular Medicine (MDC) in Germany, Imperial College London and their global collaborators. The team analyzed almost a half million individual cells to build the most extensive cell atlas of the human heart to date. The atlas shows the huge diversity of cells and reveals heart muscle cell types, cardiac protective immune cells and an intricate network of blood vessels. It also predicts how the cells communicate to keep the heart working. The research is part of the Human Cell Atlas initiative to map every cell type in the human body.