Heartin tells the story of Imaya, an IT professional who develops a close friendship with Sananth, a hotelier based in Rajasthan. As their bond turns into love, she learns about his past relationship with Madonna Sebastian. Choosing to move forward, the couple begins a new chapter, and their families even start wedding preparations. However, a sudden accident changes everything—Sananth loses his memory of recent events, including his relationship with Imaya. What follows is an emotional conflict over love, memory, and fate.