new Float:fHealth;
public Antihack()
{
    new x;
    new Float:rHealth;
    for(x=0;x<MAX_PLAYERS;x++)
    {

    GetPlayerHealth(x, rHealth);

    if(rHealth != GetPVarFloat(x, "faPlayerHealth"))
    {
      // Player health has changed since the last update -> server, so obviously thats the thing updated.
      // Lets do further checks see if he's lost or gained health, anti-health cheat? ;)

      if(rHealth > GetPVarFloat(x, "faPlayerHealth"))
      {
        /* He has gained health! Cheating? Write your own scripts here to figure how a player
            gained health! */
      }
      else
      {
        /* He has lost health! */
      }

      SetPVarFloat(x, "faPlayerHealth", rHealth);
    }
    }
}