Rory McIlroy revealed he had an "irregularity" with his heart that he would need to manage.
The Northern Irishman finished 2017 without a win – the first time he had failed to claim a tournament in a calendar year since 2008.
While McIlroy battled injuries last year, the 28-year-old revealed he also had a heart problem that he needed to keep an eye on.
"The rib's fine, no problems whatsoever – I had an MRI scan on my thoracic spine and all was OK. But I've got a bit of an irregularity with my heart that I have to keep on top of," the world's No. 11 golfer told The Telegraph. "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.
"I suffered a really bad viral infection in China 18 months ago and they told me that's the reason that I have this thickening of my left ventricle and there's a bit of scar tissue.
"For now, I just need to stay on top of it and have to stay fit. Hey, I was planning on doing that anyway."
A four-time major winner, McIlroy claimed the most recent of those at the 2014 PGA Championship.
While he has slipped outside the top 10 in the rankings, McIlroy said his focus was purely on winning.
"It's nice to be world number one, sure, and I will get back there, but it's all about winning tournaments," he said. "And I will give myself the best chances this season."