In summary, with scRNA-seq of hearts from both mouse and human and lineage tracing, we demonstrated a critical role of CD34+ cells in the process of myocardial remodeling, managed to systematically characterize the cellular landscape of myocardial fibrosis at a single-cell resolution and provide a comprehensive cell atlas including CD34+ cells, fibroblasts, endothelial cells and immune cells. Here, CD34 is linked to Myocardial fibrosis.