We studied the stochastic nature of heterogeneous nucleation of supercooled liquid water by molecular dynamics simulations. The systems were composed of 768 molecules; M of them had their positions restricted forming a solid nucleus (INM) for M=48, 56, 64, 72, 80 and 90 molecules, and the rest were arranged in liquid state. By using a statistical analysis, we determined the nucleation rate (j(M)) for systems formed with IN64, IN72, IN80 and IN90. These results are coherent with the stochastic hypothesis for heterogeneous nucleation and show a direct relationship between M and j(M). (C) 2015 Elsevier B.V. All rights reserved.