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…