(CNN) - One of the most anticipated new functions of the latest Apple Watch goes into effect Thursday.
The Apple Watch Series 4 can now perform a mobile electrocardiogram whenever a customer wants.
It can't detect all heart rhythm abnormalities, or the electrical changes associated with a heart attack, but it can help detect a condition known as atrial fibrillation.
That's when patients feel something like a fluttering in their chest.
Symptoms of atrial fibrillation often dissipate before a person can get to a doctor, so it can be difficult to diagnose.
And it's the second most common cause of death around the world.
Once the electrocardiogram function is set up, the Apple Watch can share results with physicians, too.
The feature is now available via a software update.