Apple Watch’s ability to detect atrial fibrillation has proven to be life-saving for many users, but a New York University doctor is now suing Apple over the feature. As reported by Bloomberg, Dr. Joseph Wiesel claims that Apple Watch infringes on his patent for a method to detect an irregular heartbeat.

Apple Watch can passively monitor a heart rate and provide notifications when an irregular heart beat is detected. This is a common sign of atrial fibrillation, and newer Apple Watch models also support the ability to take an electrocardiogram using the Digital Crown.

In the lawsuit, Wiesel says that his patent marked the “pioneering steps” in monitoring for atrial fibrillation detection. The patent describes how to monitor “irregular pulse rhythms from a succession of time intervals.” The patent was awarded to Wiesel in March of 2006, described as a “method and apparatus to determine possible atrial fibrillation.”

Wiesel, who currently teaches at the NYU School of Medicine, also says that he reached out to Apple in September of 2017 about a partnership, but Apple didn’t entertain his requests:

With this lawsuit, Wiesel is asking the court to block Apple from using his patented atrial fibrillation technology without permission and royalties. For its part, Apple hasn’t commented on the case and it’s unlikely that it will.

Apple has “refused to negotiate in good faith to avoid this lawsuit,” Wiesel contends in the suit

Apple has made health a top priority in recent years, particularly with the Apple Watch. Apple CEO Tim Cook has said on multiple occasions that he believes Apple’s greatest contribution to mankind will be health-related.