A novel vortex micromixer is proposed comprising an injection channel (Y-shaped or Interlaced-shaped), a nozzle structure and a double-heart mixing chamber. In the proposed device, the species are loaded into the injection channel and undergo an initial mixing effect as a result of natural diffusion. The partially-mixed species are then passed through the nozzle structure into the double-heart chamber, where they are further mixed by symmetrical rotating vortex structures before flowing into the exit channel. The flow phenomena and species concentration distributions within the nozzle structure and double-heart mixing chamber are evaluated by means of numerical simulations. The numerical results are confirmed by performing flow visualization experiments. It is shown that the mixing ratio in the Interlaced-shaped micromixer reaches 92% even at Reynolds numbers as low as Re = 1 given a nozzle ratio of 0.25. Overall, the results presented in this study show that the proposed vortex micromixer provides a simple yet effective solution for mixing problems in the micro-total-analysis systems (mu-TAS) field. (C) 2014 Elsevier B.V. All rights reserved.