After taking three top trumps, you need two fast pitches for heart losers. It is acceptable for West to be able to ruff the second of these with his trump trick, but not the first. As there is only one discard available from diamonds regardless, the contract will fail (barring West's opening lead having been a singleton) if you cannot get to lead the third round of clubs.
As you must asssume for success that West has at least two clubs, you should lead clubs before diamonds, perhaps obtaining more information. Should both opponents follow to the ace and king of clubs, you will switch to diamonds for one discard, then play the queen of clubs for the other--it is more likely by far that West will have to follow to three rounds of diamonds than that he will hold the long club. In the unlikely event that West holds four clubs (see diagram), you discard a heart on the queen of clubs, ruff a club, enter dummy with a diamond, and throw the last heart loser on an established club.