I have seen many people questioning if Lars is immortal or not based on the events of "Wanted". So let's do the math. A lot of this math is done on cursory Google searches, so keep that in mind in case I am wrong and make a fool of myself.

His heart has not stopped. However it has slowed tremendously.

By my calculations with a stopwatch app, Lars now has a heart rate of 1 beat every 2.5 seconds. This puts him at about 24 bpm, or 12,614,400 heartbeats per year, as opposed to a normal human's heartrate of 80 bpm.

If we assume the average human lifespan to be around 80 years of age, then the average amount of heartbeats per person is ~3,363,840,000. This also comes out to ~42,048,000 heartbeats per year.

If we assume that Lars is somewhere between 16 and 18 years old then he has already used up between 672,768,000 and 756,864,000 heartbeats. Lets take the average and say he is about 17 with 714,816,000 heartbeats.

Subtracting this leaves him with approximately 2,649,024,000 heartbeats remaining at his current heartrate of 24 bpm.

That means that to go through an average human amount of heartbeats will take Lars about an additional 210 years. Provided my math is correct and I am not a big dummy.

However, this does not mean he is not immortal if we are using Lion as a previous example. An average African Lion has a lifespan maxing out at about 15-18 years in the wild or 25-30 years in captivity.

The average lion has a heart rate of between 42 and 76 bpm. So let's take the average and say 59 bpm. If we apply the same rate of slowing to the heartbeat to lion as we did to Lars, that means that Lion's heartbeat is around 18 bpm.

Most non-Homo sapien animals have an average of 1 billion heartbeats per lifetime, so this is the number I am going to use since I couldn't find one for lions.

This means that if Lion supposedly died the moment he was born and was resurrected by Rose Quartz and would have lived out the maximum 30 years, his extended heartbeat lifespan would max out at 105 years. This means that if Lion is indeed one of the Lions from "Buddy's Book", then he is at least twice as old as he would have been if average heartbeats had anything to do with it and very well might be immortal.

Edit: either that, or if they aren't immortal then Lion is much younger than we were first lead to believe (totally forgot to put that in before. Whoops)

TLDR: If my math is right and heartbeats have anything to do with it, Lars will live another 210 years. But they probably don't, since by the same math Lion would have been dead about 100 years ago, so they both very well might be immortal.