Nenjathai Killathe (English: Don't Pinch the Heart) is a 1980 Indian Tamil drama film written and directed by J. Mahendran. The film stars Suhasini, in her debut film appearance, as the central character along with Sarath Babu, Mohan and Pratap Pothan in other prominent roles. The film's score and soundtrack were composed by Ilaiyaraaja while the cinematography was handled by Ashok Kumar. The film won three awards each at the 28th National Film Awards and Tamil Nadu State Film Awards in 1981. The performances of Suhasini and Sarath Babu received critical acclaim. The film was dubbed into Telugu as Mouna Geetham.
Chandrasekhar (Sarath Babu) is married to Mala (Shanti Williams) and their marital life is miserable due to Mala's demonic behaviour.
Chandrasekhar's sister Viji (Suhasini), who is brought up by him, is enthusiastic, naughty and fun-loving. She lives life on her own terms. One day she bumps into Ram (Mohan), a mechanic. Despite initial conflicts, they slowly become friends. Though good natured, Ram suffers from an inferiority complex and suspects everyone. Mala suspects that Chandrasekhar's classmate Ramya (Vanitha) is his concubine since he visits her often. Chandrasekhar learns of Ramya's love for him only after his marriage to Mala. Ramya remains single and they share a platonic relationship, which antagonises Mala. Pratap (Pratap K. Pothen) is a photographer and a distant relative of Chandrasekhar. He comes to Chennai from Calcutta and works for an agency. Though Pratap likes Viji, he does not propose to her.
Ram proposes to Viji, who is unsure whether to accept his suit. However, they become closer. Viji's harmless mischief at home with Mala intensifies when Viji mixes chilli powder in Mala's bath water as punishment for the nuisance Mala creates at home. Enraged, Mala swears revenge on Viji someday. Viji accepts Ram's proposal and informs Chandrasekhar, who advises her to reconsider her decision as he feels they are not compatible.
However, seeing her persistence, he approves. Ram's parents visit Viji's house to meet Chandrasekhar and take the proposal forward; in his absence, they meet Mala. Mala, pretending it to be a slip of tongue, lies to them about an abortion Viji had, as a result of a stray relationship.
Shocked, they inform Ram that they have heard this from a doctor (to keep the informer's identity a secret). Shocked, Ram confronts Viji and asks her to clarify, saying he would decide the future course of action based on her reply. Angered with Ram's lack of trust in her, she ends her relationship with Ram and they split.
Seeing a depressed Viji, Chandrasekhar advises her to marry Pratap, as he is mature enough for her. Initially reluctant, she eventually agrees and marries Pratap. When Viji is leaving for her new life with Pratap, she is further upset when Mala proudly declares that it was she who derailed her wedding with Ram by misleading his parents.
Post marriage, Viji is unable to accept Pratap as her husband and stays aloof since the memory of Ram's lack of trust lingers in her mind. Pratap too is not demanding and patiently waits for her to become normal. Viji is unable to forget her past, and her indifference affects Pratap's creativity and work. One day, Ram also moves in with his wife to the same apartment complex and becomes Viji's neighbour, Viji gets all the more disturbed. Pratap loses his job and plans to relocate to Calcutta.
He reserves tickets for Viji as well, but lets her decide if she wants to accompany him. When she is undecided, Ram, who is aware of the happenings, invites her to his home. He introduces her to his physically handicapped wife (whom he had married to atone for his sin in doubting Viji's character) with whom he tries to be happy now.
Ram mentions that despite his wife's handicap, he tries to live happily with her. He asks Viji why she cannot live happily with Pratap, who is more qualified and better than him in all respects, instead of thinking about their past and the grouse of losing the life she dreamt of. Realising her mistake of spoiling her present by living in the past, Viji rushes to meet Pratap who has already left for the airport. At the airport, she requests him to disembark and joins him.