This is the 2620th most frequent Russian word.
тяжелых
The Russian word "тяжелых" means "heavy" or "difficult" in English (genitive plural or accusative plural form).
The word 'тяжелых' is used to describe the intensity or difficulty of the efforts needed in this context.
Эта работа требует тяжелых усилий.
This work requires heavy efforts.
The word 'тяжелых' here describes the physical weight of the metal plates.
У него была коллекция тяжелых металлических пластин.
He had a collection of heavy metal plates.
In this sentence, 'тяжелых' refers to the emotional or psychological burden of the memories.