During seed-mediated growth, the Pd-Au nano-heterostructure can be either centrosymmetric Pd@Au core-shell trisoctahedra or asymmetric Pd-Au heterodimers. What causes the symmetry breaking of bimetal nano-heterostructures? A recent study proposes that the thermodynamic factor plays a key role for the symmetry breaking of bimetal nano-heterostructures during seed-mediated growth.