In this paper the inequality which is satisfied by the determinant of the solution of the Lyapunov matrix equation

is presented. The result makes possible a lower estimate of product eigenvalues of the matrix

and dependence from eigenvalues of the matrices

and

. This result corresponds to those presented in [2] and [3], where an estimate of the extremal eigenvalues of the matrix

is presented. This estimate depends on the eigenvalues of the matrices

and

.