The four-time major champion, who missed the latter stages of the 2017 season with a rib injury, told James Corrigan of the Telegraph his medical team said he must "stay on top of" the latest issue.
"The rib's fine, no problems whatsoever—I had an MRI scan on my thoracic spine and all was OK," McIlroy said. "But I've got a bit of an irregularity with my heart that I have to keep on top of. I have a flat T-wave and I'll have to get an echo [cardiogram] on my heart every six months and an MRI scan every year."
Health concerns aside, McIlroy sounded an extremely optimistic tone about once again establishing himself as one of the sport's top contenders, proclaiming: "Maybe before, I had to win from the front. I just don't feel that now. I don't fear any of them. Any one of them. I've beaten them before."
"It's nice to be world No. 1, sure, and I will get back there, but it's all about winning tournaments," he told Corrigan. "And I will give myself the best chances this season."
The 28-year-old Northern Irishman failed to win an event in 2017. He did finish second in two European Tour tournaments, the BMW SA Open and British Masters, and recorded five top-10 results on the PGA Tour, including at the Masters (seventh) and The Open Championship (fourth).
His time away to recover from the rib ailment—his last appearance was the Alfred Dunhill Links Championship in early October—dropped him to 11th in the World Golf Ranking. That represented his lowest year-end rank since 2008 (39th).
McIlroy will return to action in the Abu Dhabi HSBC Golf Championship starting Thursday at the Abu Dhabi Golf Club in the United Arab Emirates.