We establish boundary regularity results in Hölder spaces for the degenerate parabolic problem obtained from the Heston stochastic volatility model in Mathematical Finance set up in the spatial domain (upper half-plane) H = R × (0, ∞) ⊂ R 2 . Starting with nonsmooth initial data u 0 ∈ H, we take advantage of smoothing properties of the parabolic semigroup e −tA : H → H, t ∈ R + , generated by the Heston model, to derive the smoothness of the solution u(t) = e −tA u 0 for all t > 0. The existence and uniqueness of a weak solution is obtained in a Hilbert space H = L 2 (H; w) with very weak growth restrictions at infinity and on the boundary ∂H = R × {0} ⊂ R 2 of the half-plane H. We investigate the influence of the boundary behavior of the initial data u 0 ∈ H on the boundary behavior of u(t) for t > 0.