  Using the techniques of isolated horizon formalism, we construct the space of
solutions of asymptotically flat extremal black holes in N=2 pure supergravity
in 4 dimensions. We prove the laws of black hole mechanics. Further,
restricting to constant area phase space, we show that the spherical horizons
admits a U(1) Chern- Simons theory. Standard way of quantizing this topological
theory and counting states confirms that entropy is indeed proportional to the
area of horizon.
