The only sound to be heard is their somewhat heavy breathing.

唯一能听到的声音是他们有点沉重的呼吸声。

youdao

I could hear his heavy breathing.

我听得见他粗重的呼吸。

youdao

Many masks aren't good for heavy breathing such as I would do while running.

有些口罩在呼吸沉重的时候，比如跑步的时候，戴着不是很适合。

youdao

Matron herself was short and stout, pink-faced, with rimless glasses and heavy breathing.

NEWYORKER: Amundsen

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Over the following nine minutes, air traffic controllers frantically tried to make contact with the cockpit, from which only heavy breathing and electronic noises could be heard before the microphone finally went dead.

BBC: Australian 'ghost flight' still a mystery