  Let $L$ be a self-adjoint invertible operator in a Hilbert space such that
$L^{-1}$ is $p$-summable. Under a certain discrete dimension spectrum
assumption on $L$, we study the relation between the (regularized) Fredholm
determinant, $\det_{p}(I+z\cdot L^{-1})$, on the one hand and the zeta
regularized determinant, $\det_{\zeta}(L+z)$, on the other. One of the main
results is the formula
  \begin{equation*}
  \frac{\det_{\zeta} (L + z)}{\det_{\zeta} (L)} = \exp \left( \sum_{j=1}^{p-1}
  \frac{z^j}{j!} \cdot
  \frac{d^j}{dz^j}
  \log \det\nolimits_{\zeta} (L+z) |_{z=0} \right) \cdot \det\nolimits_{p}(I +
z \cdot L^{-1} ).
  \end{equation*} We show that the derivatives $\frac{d^j}{dz^j} \log
\det\nolimits_{\zeta} (L+z) |_{z=0}$ can be expressed in terms of (regularized)
zeta values and heat trace coefficients of $L$. Furthermore, we give a general
criterion in terms of the heat trace coefficients (and which is, e.g.,
fulfilled for large classes of elliptic operators) which guarantees that the
constant term in the asymptotic expansion of the Fredholm determinant,
$\log\det_{p} (I+z\cdot L^{-1})$, equals the zeta determinant of $L$.
