The soldier did not intend his own death. Nor was saving the others a direct result of the death. His intent was to block the grenade, a neutral act, to save the many others. His death was an unintended (but foreseen) side effect that was outweighed by saving many lives.
We know that losing his own life was not his intent and merely a side effect because he wouldn’t have cared (and in fact would have preferred) if he could have stopped the grenade without his death. If jumping on the grenade had merely caused him survivable harm…he would have still done it. It was not his death specifically that was necessary to stop the grenade, just some form of blocking it. The grenade being blocked was not the result of his death, rather, his death was the result of the grenade being blocked. The order of causation in this situation is acceptable: the cause (his body blocking grenade) was neutral and the good results of this neutral action (saving lives) outweighed the bad (his death from the injuries).
However, killing oneself to give an organ doesnt work out that way. When someone kills themselves to give an organ (especially by just taking pills beforehand like the guy on House…but even if the death happens on the operating table intentionally) the death is the cause of the organ transplant with certain organs.
The heart being removed IS death. The person can’t say, “Well, the intention was to remove the heart, a neutral action, with the good effect saving lives with the organs outweighing the unintentional death of the patient.” No, removing the heart permanently IS killing, not a neutral act, but an intrinsically evil act. Someone cannot plausibly say that the death isn’t the cause of the good, merely a side effect of a previous neutral action leading to both. What neutral action would this be? “Removing the heart” is not a neutral action with the unintended side effect of killing, it IS killing. The soldier could have at least imagined surviving, as long as he saved his comrades, he didnt particularly want to die, he would have been fine with the possibility of merely being injured, not killed. But no person giving away their heart while they are still alive can entertain the notion that their death is merely a “side effect”. No, “Death” and “heart removal” are basically the same action. In the soldier case you can truly abstract “blocking the grenade” seperate from “death” (maybe he will merely be injured). But “heart removal” cannot be reasonably abstracted from “death”…Maybe someday when permenant artificial hearts are invented, but not now.