Mr. Pack,

According to prisoner-of-war records, Andrew J. [A. J.] Funk was scheduled to be sent to Aiken's Landing for exchange on October 29, 1864. Unfortunately, he died on October 20th from "Chr. Val. Dis. of Heart". I'm not a medical expert but that is probably chronic valve [valvular] disease of the heart.

See:
http://www.pdrhealth.com/disease/disease-mono.aspx?contentFileName=BHG01CA16.xml&contentName=Heart+Valve+Disease&contentId=70

Heed the sound advice of Mr. Martin and Mr. Pitts- order the compiled service records and examine them for yourself.