  We design a Mixed Virtual Element Method for the approximated solution to the
first-order form of the acoustic wave equation. In absence of external load,
the semi-discrete method exactly conserves the system energy. To integrate in
time the semi-discrete problem we consider a classical theta-method scheme. We
carry out the stability and convergence analysis in the energy norm for the
semi-discrete problem showing optimal rate of convergence with respect to the
mesh size. We further study the property of energy conservation for the
fully-discrete system. Finally, we present some verification tests as well as
engineering application of the method.
