Abstract: Antibodies which bind selectively to cardiac conduction system (CCS) cells, imaging and/or diagnostic reagents and compositions visualizing the CCS cells and therapeutic products and compositions comprising one or more of the antibodies. Methods for delivering therapeutic agents to the CCS cells. The disclosure further provides methods for visualizing the CCS cells in vivo in real time, including in a subject undergoing a cardiothoracic surgery or other cardiac intervention. Compositions and methods for isolation, purification, analyses and/or transplantation of the CCS cells, including pluripotent stem cell (hiPSC)-derived or human embryonic stem cell (hESC)-derived CCS cells.