A bag for mixing fluid volumes includes a port at a center of a first end, a second end, a first constriction, and a second constriction. The port is configured to couple to at least one fluid line for introducing and removing fluids from the bag. The second end includes a first lobe and a second lobe. The first constriction is on the first side between the first end and the second end and the second constriction is on a second side between the first end and the second end.