This magnesium-dependent enzyme catalyzes the hydrolysis of ATP coupled with the transport of calcium. Transports calcium ions from the cytosol into the sarcoplasmic/endoplasmic reticulum lumen. Contributes to calcium sequestration involved in muscular excitation/contraction. {ECO:0000269|PubMed:11956212, ECO:0000269|PubMed:15028735}. This is the function of ATP2A3 (ATPase sarcoplasmic/endoplasmic reticulum Ca2+ transporting 3, ENSG00000074370).