My Bloody Valentine (1981)

On Valentine's Day 20 years before, an explosion of methane gas took the lives of a group of miners working in the Hanniger Mine. The accident occurred because supervisors left their posts to attend the annual Valentine's Day dance. A year afterward, Harry Warden - the only survivor of the accident - retaliated by killing the two supervisors, and leaving a terrifying warning never to hold another Valentine's Day dance. Now, a group of young adults decides to hold another dance, despite warnings. When a blood-soaked heart arrives at the police station, accompanied by an ominous message, the dance is cancelled. But a Valentine party is held in its place, and it isn't long before the town's young people begin dying violently. It appears Harry Warden has returned to punish those who did not heed his warning...