The 31-year-old actress and 46-year-old Tesla founder recently called it quits due to their busy schedules, according to Us Weekly.
"The timing wasn't good for them," a source told the magazine. "He's super busy and works all the time. Amber is filming [Aquaman] in Australia until October. She's in no position to settle with him. She feels her career is just starting."
Heard and Musk met on the set of Machete Kills in 2013, and were first linked in July 2016 following their respective splits from Johnny Depp and Talulah Riley. The actress spent time with Musk and Riley's five sons in Australia in May.
"Elon and Amber are already very serious about each other," a source told People the same month.
Heard has yet to address the breakup, but shared photos late Sunday night of herself enjoying a "BBQ dance party" with friends. She will play Mera in Aquaman, which stars Jason Momoa as the title character.
"She wanted to deliver for the character," Heard's personal trainer Gunnar Peterson told People in June while discussing the star's intense training regime. "She is a true athlete."
Heard will debut as Mera in Justice League before reprising the character in Aquaman, which opens in theaters in December 2018. She will also star in London Fields with Cara Delevingne and Billy Bob Thornton.