Comment Or maybe heart shape is distorted by gravity (Score 1) 113
If hearts became more rounded through increased muscle mass then that could be evidence that hearts performance inefficiently in zero-g. Unfortunately, the teaser articles doesn't say that. Just changing shape could simply mean that heart development is normally distorted by gravity and without gravity, you naturally get a more rounded shape. A third possibility is that the longer shape is muscle mass needed to counteract gravity. Without gravity, there is no need so that extra muscle is lost. I suppose that could be a form of inefficiency since it means that heart is overbuilt for the task.
I might be interesting to study the hearts of hearts of people who stay horizontal. Generally these with be comatose or otherwise bed-ridden without sitting up. Not a perfect analogy, though, since these patients are not getting any exercise while the astronauts are.