forward ...
new...

public OnPlayerHealthChange(playerid, Float:newhealth, Float:oldhealth)
{
  do something lots...
}
public OnPlayerUpdate(playerid) 
{
	if(IsPlayerConnected(playerid))
	{
		GetPlayerHealth(playerid, iNewPlayerHealth[playerid]);
		if(iNewPlayerHealth[playerid] != iPlayerHealth[playerid])
		{
		  OnPlayerHealthChange(playerid, iNewPlayerHealth[playerid], iPlayerHealth[playerid]);
		  iPlayerHealth[playerid] = iNewPlayerHealth[playerid];
		}
	}
}