Apex domains cannot have CNAME records.
Question and response
Question
dig floridaheartlung.com. NS
Answer
floridaheartlung.com. 5 NS ns-103.awsdns-12.com.
floridaheartlung.com. 5 NS ns-1677.awsdns-17.co.uk.
floridaheartlung.com. 5 NS ns-190.awsdns-23.com.
floridaheartlung.com. 5 NS ns-1958.awsdns-52.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0