Is hard work is a work heading towards Heaven?

Not really. Just working hard does not assure you entry into heaven. You might be working hard but in the process you neglect other things like your family, your relationship, your spiritual obligations and so instead of gaining merits you would be earning more demerits. Also, if i'm not mistaken, it is faith together with good works (not hard work) which paves the way into heaven or assures salvation. good works means doing good for your fellowmen, charitable acts, helping hands, kindness, being merciful, forgiving, kind in accordance with the teachings in the HOly Book.