Charlie Beljan has taken a three-stroke lead at the end of the second round at the Children's Miracle Network Hospitals Classic in Lake Buena Vista in Florida.
However, the 28-year-old, who suffers from asthma, was rushed to hospital with heart palpitations at the end of play.
Beljan was forced to take rest on several occasions because of an elevated heart rate and shortness of breath, but that did not deter the American from posting two eagles, six birdies and two bogeys on his way to a three-shot lead on 12-under-par 132.
Overnight leader Charlie Wi is among seven players who are three strokes behind Beljan.
Wi, who had ended the first day on 64, recorded a one-under-par 71 on Friday with five birdies and four bogeys.