How can you recognise heart problems in horses?

Panic at the European Football Championships last Friday: during the match between Denmark and Finland, star player Christian Eriksen suddenly collapsed. Afterwards, the team doctor confirmed that the Dane had a heart attack on the field. The scene brought back painful memories of when Eric Lamaze's top horse Hickstead collapsed after the course and died on the spot due to a cardiac rupture. "Top horses, like footballers for that matter, are tested regularly. Before a horse can be considered 'fit to compete' at a tournament such as the Olympic Games, it has to undergo numerous tests," says an equine cardiologist. But how can you, as a 'normal rider', recognize heart problems in your horse at an early stage?