A comprehensive resource of single-cell transcriptomes of both CMs and non-CMs from normal, failed, and recovered human heart was constructed. ACKR1+ ECs with a protective function decreased in failed hearts. Injection of ACKR1+ ECs rescued cardiac function after MI by increasing vessel density in both infarct and border region in mice. The gene discussed is ACKR1; the disease is myocardial infarction.