'90 Day Fiancé' Star David Murphey's Cause of Death Revealed

'90 Day Fiancé' star David Murphey passed away last week ... and now we've learned more details about his death.

A Clark County, Nevada spokesperson tells TMZ ... the reality TV star, who was best known for appearing on "90 Day Fiancé: Before the 90 Days," died from heart-related problems -- including cardiac arrhythmia and hypertensive cardiovascular disease.

We're told David also had a history of pulmonary embolism -- which occurs when a blood clot in a lung creates a blockage. Following these findings, David's death has been ruled as a natural one.

This update comes a day after David's family announced his passing on social media ... where they revealed the TV personality had faced a number of "health issues over the last several years."

Sources with direct knowledge told TMZ at the time ... David had also been battling liver cancer before his death -- he was diagnosed more than a year earlier. Though, sources said at the time that DM faced a series of other health issues ... which seemingly led to his death at age 66.

David was best known for appearing on '90 Day Fiancé' alongside Lana, his then-girlfriend from Ukraine ... who David dated online for 7 years before meeting in person for the first time on the show.

The pair did get engaged while filming 'Before the 90 Days' ... but the engagement did not last long.

David's family -- including his 2 sisters -- have called on fans to honor DM by donating to The Animal Foundation in Las Vegas in his name ... as he was a known cat rescue advocate.