To lose hope, courage, or eagerness; be very disappointed.
Терять надежду, мужество; быть очень разочарованным.
My heart sank when I heard the news about the accident.
У меня замерло сердце, когда я узнал о несчастном случае.
My heart sank when I saw the amount of work waiting for me.
Когда я увидел, то количество работы что мне предстояло сделать, настроение сразу испортилось.
The children were happy because they were going to the beach to swim, but their hearts sank when it began to rain.
The soldiers' hearts sank when they saw that they were surrounded by Indians.