This is the first of three exercises following the article 'Ruffing: sometimes it's good... but sometimes it isn't ***, which has been published earlier.
To read that article, click Ruffing at bridge play. 

N/All		♠	J
		♥	J 8 2
		♦	9 7 5 4 3
		♣	A 8 7 3
		♠	A K Q 7 6 5 4
		♥	7 6
		♦	A K
		♣	6 4

West leads the ♥9 to East's ♥Q. East continues with the ♥K (West contributing the ♥3) and the ♥A.
How should South play?

Solution

West obviously had a doubleton in hearts, so declarer has to watch his step. If he ruffs in South with a low trump, West is very likely to overruff. But if South ruffs with a high trump, he will subsequently lose a trump trick if the trumps are 4-1. In both cases he will be down one, since there is an inescapable club loser.
So, in the lay-out below he will go down, whether he ruffs high or low:

N/All		♠	J
		♥	J 8 2
		♦	9 7 5 4 3
		♣	A 8 7 3
♠	10 9 8 3			♠	2
♥	9 3			♥	A K Q 10 5 4
♦	Q 10 8 6			♦	J 2
♣	Q 9 5			♣	K J 10 2
		♠	A K Q 7 6 5 4
		♥	7 6
		♦	A K
		♣	6 4

The solution: South does not ruff, he discards his club loser (loser on loser).
It's not over yet: East will play a fourth round of hearts. Declarer now ruffs low in hand. This way West cannot wriggle out if he has four trumps: if he overruffs, dummy in turn will overruff him and the ♠AKQ pick up West's remaining three trumps. If West does not overruff the fourth heart, declarer can draw all of West's four trumps with the ♠J and the ♠AKQ.
Declarer will only be defeated in the unlikely case that West has a singleton ♠10, ♠9 or ♠8. He will then overruff South and dummy will overruf West with the ♠J. East will subsequently make a trump trick from his four card suit. Declarer is powerless against that — very unlikely — distribution.

For exercise 2, click: Ruffing at bridge play- Exercise 2.