“I did a test in pre-season and found out I had a hole in my heart and when you hear that you think the worst. But, they reassured me, I’ve had it my whole life,” Hayes explained to AFL.com.au.
“I haven’t had any symptoms or anything like that, but they said look you’re better to get it fixed now rather than wait another year or two.
“I’m glad they’ve found it, it feels really good, fingers crossed I don’t have any lingering effects from it.”
The St Kilda veteran revealed his “fairly major operation” actually had less of an impact on his preparations than calf and hamstring woes in years gone by.
“I’ve been back in full training probably about three months now,” Hayes said.
“I had a modified program for probably the first month, but since then I’ve been doing everything and all the contact drills, all the grappling, every session I’ve pretty much done. "
Hayes said he’ll probably be in a position to play in three of the four upcoming NAB Cup rounds.
“I feel ready to go, and there’s nothing that I really have to do in terms of maintenance and or anything like that.”
The 33-year-old said the whole experience had taught him a lot.
“You certainly have an appreciation for people who’ve been through that,” Hayes said.
“I saw kids who had a similar operation to me, and it’s a pretty traumatic thing for a kid to go through."
Hayes believes St Kilda can show up its critics and reach the finals this year, after missing out in 2012.
“It’s a little bit of the unknown, and I guess we sit in that category a little bit as well.
“I think all things going well, we play our best footy, I think it stacks up, so I’m hoping that we’ll be playing some games in September.”
Matt Thompson is a reporter for AFL Media. Follow him on Twitter @MattThompsonAFL