Regarding your question about the jiva soul in the heart and the jiva soul within the cells, they are separate. Both are jiva atmas, but a particular jiva belongs to a particular body. There is the jiva in this body, but there are also jivas within the cells. Just like I am living within this apartment, but does it mean that no other living entity can live here. There are so many ants, flies, bugs, they are also living within the apartment. Even in my stool there are thousands of living entities.
Letter to Svarupa Damodara dasa, 23 June, 1975