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

Endurance: Seniors should try to get at least 30 minutes of activity that causes heavy breathing almost every day.

CNN: The new face of fitness is getting older

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

Ms. LITHWICK: Well, what he says is he's very concerned, and it's important to bear in mind he has rejected such claims before, he's saying that recent accounts of death row inmates who suffer episodes of very heavy breathing, of heaving chests, long, long periods of time when it's clear that they are not yet anesthetized, concerns him, and he cited specifically the Stanley Tookie Williams execution.

NPR: Slate's Jurisprudence: Cruel, Unusual Injections?