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Over the past year, Apple Watches have been credited with detecting heart complications and saving lives on multiple occasions.

Now, a doctor from New York University is suing the tech giant over the feature that made it all possible.

Cardiologist Joseph Wiesel claims that Apple used his patented heartbeat-monitoring technology and integrated it into Apple Watches after he told the tech company about his invention in September 2017, Bloomberg reports.

Wiesel was granted a in 2006 for a "method of and apparatus for detecting ." Atrial fibrillation, or AFib, is an irregular and often rapid heart rate that causes about 750,000 hospitalizations each year, according to the CDC. Wiesel's patent uses sensors and light to detect heart rhythms, which can then be shown on a digital display.

In a lawsuit filed Friday, the plaintiff alleges he sent details about the patent to Apple after it released its Series 3 smartwatch. A year later, the iPhone maker unveiled its Series 4 with AFib detection.

Earlier versions of the smartwatch got updates to include heart-monitoring features, as well.

Apple's smartwatches don't outright diagnose medical conditions. Instead, they offer notifications if an abnormal heartbeat is detected.

Wiesel is demanding that Apple pay him royalties for embedding his into smartwatches. He also wants the California-based company to stop using his patent without permission.

In court documents, Wiesel said Apple "refused to negotiate in good faith to avoid this lawsuit." He also alleges that Apple knows that his intellectual property is pertinent to its business strategy.

Apple Watches have become a market leader in the wearables category and generated more than $24 billion in sales in the fiscal year that ended in September, Bloomberg reports. Apple accounted for more than a quarter of all wearable devices shipped in 2018, according to International Data Corp. data.

The tech company doesn't comment on ongoing litigation.