Bodybuilding Influencer Dead at 48 After Heart Attack

International bodybuilder Einar Méndez died from a "sudden heart attack" after collapsing ... his wife revealed in a heartbreaking social media post.

The fitness influencer -- who boasts 47,000 followers -- was declared dead on Sept. 4 after a workout session at his Mexico City gym, according to his wife Yan Méndez. He was only 48.

Yan wrote on Instagram ... "Rest in peace, love of my life. Fly to the highest heights, and I promise we will meet again."

The couple -- who were set to travel to New York City for the first time soon and had just celebrated their 30th anniversary -- welcomed three children together ... Fanny, Frida, and María Regina, according to Mexican publication El Heraldo.

In addition to his bodybuilding career, he was also a coach to local celebs ... including television presenter Martha Debayle.

She wrote ... "We are all still in shock. He left suddenly, in the gym, doing what he loved most: training."

After nine years of working together, Martha said "there won't be a single day that I train and don't think" of Einar.

Einar was 48.