Complex sentence: The largest part of the heart is usually slightly offset to the left (though occasionally it may be offset to the right) and is felt to be on the left because the left heart is stronger, since it pumps to all body parts.
Split into simpler sentences: The largest part of the heart is usually slightly offset to the left (though occasionally it may be offset to the right). The heart is usually felt to be on the left side because the left heart is stronger, since it pumps to all body parts.