Which of the following plants has heart-shaped leaves and violet flowers?

The plant that has heart-shaped leaves and violet flowers is indeed the violet. Violets belong to the genus Viola and are well recognized for their distinctive foliage and blooms. The heart-shaped leaves are typically a defining characteristic, and the flowers can appear in various shades of violet, making them easily identifiable.

Knotweed, prostrate spurge, and broadleaf plants do not share these particular traits. Knotweed has elongated, narrow leaves and does not typically feature violet flowers. Prostrate spurge is characterized by its fleshy, small leaves and yellowish-green flower clusters, which do not resemble violets. Broadleaf generally refers to a category of plants with larger, flat leaves and does not specifically describe a single species with the same identifiable characteristics as violets. Thus, the defining features of heart-shaped leaves and violet flowers distinctly point to the violet as the correct answer.