We have studied the spatiotemporal dynamics of the electrodissolution of an iron ring under potentiostatic conditions in a region of parameter space in which active-passive transitions occur. The current (proportional to the overall dissolution rate) is measured as a function of time; patterns (due to growth and dissolution of surface films) are recorded with a microscope and a video camera. We observe the following spatiotemporal features as a parameter, the potential, is changed : (1) the current oscillates periodically and the passivation occurs through the growth of a symmetric film which propagates radially; (2) the symmetry breaks giving rise to a period-doubled oscillation in which activation-passivation occurs on alternate half sections of the ring; (3) this symmetry is broken resulting in patterns on four quadrants of the ring.