Prince's Sister Tyka Nelson Cause of Death Revealed, Cardiac Arrest

Prince's sister Tyka Nelson suffered congestive heart failure when she died ... but authorities say her heart was also weakened by substance abuse.

The Minnesota Dept. of Health issued Tyka's death certificate, which lists cardiac arrest as the primary cause of death, and congestive heart failure as the secondary cause.

According to her death certificate, the 64-year-old singer and songwriter suffered cardiac arrest about 45 minutes before she was pronounced dead. She'd also battled non-ischemic cardiomyopathy -- a general term for abnormal heart function -- for more than 4 months.

Tyka died on November 4 in the Minneapolis/St. Paul area, and as TMZ first reported ... she'd been dealing with heart problems for several years. We discovered paramedics had been called to her home at least 6 times since September.

Her death certificate also lists "substance use disorder" as a contributing condition in her death, but the document does not list any specific substance.