Silicon Valley executive Dave Goldberg died in a gym during an exercise session, a source close to his family said.
Goldberg, 47, who was chief executive of SurveyMonkey and married to Facebook executive Sheryl Sandberg, collapsed on holiday in Mexico. "Efforts to revive him at the gym and at a hospital were unsuccessful," the source said.
No comment on his death has yet been made by Sandberg. His brother Robert announced Goldberg's "sudden" death on Facebook and asked for condolences and memories to be posted on the father-of-two's page on the website.
Goldberg's death prompted a flood of tributes from fellow digital chiefs. Facebook chief Mark Zuckerberg said: "Dave Goldberg was an amazing person and I am glad I got to know him. My thoughts and prayers are with Sheryl and her family."
Meanwhile, Huffington Post founder Arianna Huffington called Goldberg an "innovator".
She said: "So deeply saddened and shocked by the death of Dave Goldberg. I was blessed to get to know him through his beloved wife Sheryl and to see first-hand what an amazing father, son, innovator and caring friend he was."
Reports said a private funeral and memorial service is planned to take place in California.