According to the Office of the Medical Examiner in Daytona Beach, Florida ... Dimitri's official cause of death is listed as a combination of fentanyl and diazepam toxicity. He also suffered from cardiomegaly ... an enlarged heart -- and had moderate coronary artery disease.

The report also lists the cause of death as an accident following "illicit drug abuse with prescription drug use." It's interesting ... the report also says Dimitri "sustained injury by electrocution [at 220 volts] while at work several days prior to being found dead at his home" but the medical examiner ultimately excluded a delayed arrhythmia from the electrical shock as a cause of death.

The report also stated Dimitri had long-standing prescriptions for hydrocodone and diazepam, but could not confirm a prescription for fentanyl.

TMZ broke the story ... Dimitri died back in April and it came as a complete shock to his family. Dimitri's family was worried after not hearing from him for several days. Dimitri, who played Uri in "Chernobyl Diaries," also had roles in "Get Smart" and "Indiana Jones and the Kingdom of the Crystal Skull."

He was 52.