Mediates the exchange of one Ca(2+) ion against three to four Na(+) ions across the cell membrane, and thereby contributes to the regulation of cytoplasmic Ca(2+) levels and Ca(2+)-dependent cellular processes (PubMed:8659820). Contributes to Ca(2+) transport during excitation-contraction coupling in muscle (PubMed:8659820). In a first phase, voltage-gated channels mediate the rapid increase of cytoplasmic Ca(2+) levels due to release of Ca(2+) stores from the endoplasmic reticulum (PubMed:8659820). SLC8A1 mediates the export of Ca(2+) from the cell during the next phase, so that cytoplasmic Ca(2+) levels rapidly return to baseline (PubMed:10967099). Required for normal embryonic heart development and the onset of heart contractions (PubMed:10967099). Ca(2+)(in) + 3 Na(+)(out) = Ca(2+)(out) + 3 Na(+)(in) Activated by micromolar levels of Ca(2+). Detected in heart, kidney and brain (at protein level). At 9.5 dpc, expression is restricted to the embryonic heart, and is not detectable in any other part of the body. The cytoplasmic Calx-beta domains bind the regulatory Ca(2+). The first Calx-beta domain can bind up to four Ca(2+) ions. The second domain can bind another two Ca(2+) ions that are essential for calcium-regulated ion exchange. Complete embryonic lethality at about 9.5 dpc. At 9.5 dpc, mutant embryos display strongly decreased body size, an absence of blood vessels in the vitelline sac, and defective heart beat. Contrary to wild type hearts that show regular contractions, about 70% of the mutants have no spontaneous contractions of the heart, and the remainder show only very slow and arrhythmic heart contractions. Mutant hearts have thinner ventricles, contain fewer cardiac myocytes, and display an increased number of apoptotic cells. Mutant hearts do not show fast Ca(2+) transients and display lack of sodium/calcium exchange activity. In mutant hearts, caffeine stimulates normal release of intracellular Ca(2+) stores from the endoplasmic reticulum into the cytoplasm, but the subsequent decrease of the high cytoplasmic Ca(2+) levels is impaired (PubMed:10967099). At 9.5 dpc, embryonic cardiomyocytes show severe disorganization of the myofibrils and swollen mitochondria (PubMed:12781968). Belongs to the Ca(2+):cation antiporter (CaCA) (TC 2.A.19) family. SLC8 subfamily.