Yes - to a degree.
Sagging breasts are normal. The following options can help:
Chest exercises will not make much of a difference if the muscles are hidden under a thick layer of fat. Weight loss can result in less fat around the surrounding areas, making your breasts appear to stand out (appear perkier) than before. The breasts will also be less heavy (due to less fat), and this can result in less sagging.
Training the pectorals The pectoralis major and minor (the chest "pecs") are the muscles that lie directly underneath the the breasts. As these muscles get bigger, they can push breast tissue upwards and outwards, providing visual volume, and resulting in a "perkier" appearance. The effect will be mitigated the larger your breasts are.