As I had written previously few times, I had met Zatopek and his wife Dana several times, talked to them and lived not far from their house. From reading and talking to him personally, I know that he had only good things to tell about his friend Vladimir Kuts. It might have been encouraged by the overall athmosphere of those times (Soviet friendship was "cool", if not desired), but he was really fond of him. On the topic of drugs, he said reluctantly that it might have been a possibility in Kuts'es case. He did not point specifically to amphetamines but described those "enhancers" as if they were them. He said that he was present and ran parts of the workout with Kuts in Melbourne before the Games and he was given special drink solutions even during the session- always prepared by his coach. Then suddenly phhhhhhhew- he was away- speeding up from 66-68s quarters to 60-62s... But Zatopek never accused Kuts from anything- he just said that it was different era with different rules and athmosphere.
Now, it is only my speculation, but amphetamines might have caused the heart enlargement and the stiffening of the contracting muscles in the heart and thus contribute to overall health deteriorientation of this great (former) Soviet (Ukrainian) runner.