Cummings, 35, is the daughter of the world's most famous arms dealer, the billionaire Sam Cummings, who died two weeks ago.
She admitted shooting Roberto Villegas, her lover, in the kitchen over breakfast last September. But she claimed that Mr Villegas, a polo-player, was a violent and dangerous man who had repeatedly threatened her, and said she was in fear of her life. She said she shot him in self-defence.
The prosecution claimed that she had murdered him in cold blood after the affair went sour. "You just flat blew him away," Kevin Casey, the prosecutor, said in his closing statement.
She had cuts on her arm which she said were caused by Mr Villegas, but experts said that they appeared to have been self-inflicted. Blood on Mr Villegas' jeans showed that he was sitting down when four 9mm bullets from a Walther pistol hit him. He still had a piece of croissant in his mouth.
Mr Casey told jurors to ignore evidence about Mr Villegas' violent behaviour. "None of that matters," he said. "It could have been Jack the Ripper ... but that did not give her the right to do what she did."
"I am very happy," Cummings told a news conference after the trial. She could have faced up to 10 years in jail for the charge of voluntary manslaughter, and served life if found guilty of first-degree murder.
Cummings is unlikely to find it hard to pay the fine. She lives on a luxurious $2bn estate in Virginia's horse country.Reuse content