May be OK for Basic Med, but if for one of the classes, omitting that on form is cause for denial and possible action I think.
No, not for Basic Med, either. Cardiac surgery is one of the conditions listed in 14 CFR 68.9 requiring Special Issuance of at least a Third Class medical subsequent to the surgery before going on Basic Med.
What the FAA don’t know - in other words, I’ve been down that road of being truthful with them and I was grounded for 6-9 months due to their lack of having licensed cardiologist on their staff. I recommend not telling them anything if your heart doctor doesn’t prohibit you from driving on our highways
Lying to the Feds is a really, really bad idea, potentially punishable by large fines and years of imprisonment if they catch you (see 18 USC 1001 and the verbiage at the bottom of the application) as well as having your pilot and medical certificates revoked, not to mention denial of any insurance claims if you have an accident. And despite what Richard said earlier, the FAA and DoJ have gone after people for lying on their medical applications. Also, remember that Martha Stewart went to jail not for the securities violations the Feds originally thought she'd committed, but for violating 18 USC 1001 by lying to them during that investigation about what she'd done even though what she'd actually done was legal.
I had no problems getting my Basic Med just 7 weeks after surgery! The post-surgery echo-cardiogram was fine and my cardiologist wrote my primary care physician a note stating that he had no concerns about her signing off on my Basic Med which she did. I am attaching my form on which the surgery is mentioned along with the medical exam dates. Feel free to reach out if I can answer any additional questions (firstname.lastname@example.org). I hope this helps, good luck and I hope you'll be flying again soon!
Basic Med FAA 8700-2 Form.pdf