Myles' cousin, Donald Holley, said he suffered a heart attack Wednesday in Miami.
Myles, a third-round pick from Florida, played six seasons with the Cowboys, winning three Super Bowl titles. Myles, a backup linebacker, started 11 games during the 1995 season. He suffered a torn ACL in the Cowboys' Super Bowl XXX victory over the Pittsburgh Steelers.
His NFL career ended the next season.
At Florida, Myles was a team captain and first-team All-SEC pick as a senior in 1990.
Calvin Watkins covers the Cowboys for ESPNDallas.com.