Cujo (1983)

Donna Trenton is a frustrated suburban housewife whose life is in turmoil after her husband learns about her having an affair. Brett Camber is a young boy whose only companion is a Saint-Bernard named "Cujo", who in turn is bitten by a rabid bat. Whilst Vic, Donna's husband is away on business, and thinking over his marital troubles, Donna and her 5-year-old son Tad take her Pinto to Brett Cambers' dad's car shop... the car fails, and "Cujo" is very, very sick...