Well, I’ll give you just two reasons that make it seem highly unlikely, then I’m done.
1) You can’t just pick a random person to murder and take their heart for a transplant. You’d have to somehow pick a compatible donor. Which means essentially you’d have to murder one of the person’s close relatives; a daughter, son, sister or brother. That’s the only way you’re guaranteed to pick someone who is likely to be compatible.
2) Say we forget all these problems and somehow your organ transplant scenario is plausible. Why remove the spleen? The only time spleens are usually transplanted is when they are part of a “multivisceral graft”, which usually means they are transplanted along with other organs in the digestive system, like intestines, liver, stomach or pancreas. Yet none of those organs were removed. So we can rule that out. Thus the spleen removal would seem inexplicable under this scenario.