The State Appeals Court has upheld a felony assault conviction against a Mankato man charged with severely injuring his infant son nearly five years ago. Thirty-one-year-old Robert Heck was convicted in Olmsted County Court last year and sentenced to 14 years in prison. Heck was accused of causing serious injuries just weeks after the baby was surgically separated from his conjoined brother at St. Mary’s in November 2006. Mayo Clinic doctors determined the infant had suffered multiple rib and leg fractures. Heck and his former girlfriend Valerie James later lost custody of the twin boys. James ended up pleading guilty to child neglect and was placed on probation.