Red fruits help keep your heart strong. is there any error?
i think the \"keep\" to be preceded by \"to\"......
Red fruits help to keep your heart strong.
is it so?

Yes.

How about this sentence: red fruits keep your heart strong. Will this change the original meaning of the former sentence? And is this sentence right?

It changes the meaning greatly.

red fruits help keep your heart strong. While they are of benefit, you also need a healthy diet and exercise, and you must watch your cholesterol levels and blood pressure.

Don't bother with all that healthy diet, exercise, low cholesterol levels and blood pressure malarky. Just eat red fruits - they keep your heart strong.

malarky : nonsense