Leosydas's wounds in the eyes of modern medical science would have been seen as trivial, being treatable with just a simple few bags of blood and a few injections of antibiotics.
And if that was too much, even a make-shift tourniquet might have worked, something to tightly wrap around the chest and forcefully bind the wound together so that blood could not leak.
Any such rudimentary techniques might have saved him.
But given he did not have this available to him, Leosydas was forced to enter the domain of death, perhaps accelerated by how seeing his friend's deteriorating condition, Perseus had even sped up his march, trying to reach his camp as soon as possible so that Leosydas would get his treatment faster.
But it was to no avail.
For by the time they reach the camp, at around the late afternoon, Leosydas had already bled for too long and was long cold and dead.