"Your heart is laboring too hard and you may be in danger."

His heart labored; shuddering ran through him like a crisis.

His heart labored as if he were fighting for his life.

Her heart labored for several beats before she was able to find her voice.

The heart still labored, but the river had slowed to a trickle.

His heart labored under a hope he didn't dare tender.

And, with it, set off excitedly, his heart laboring, for the level below.

My heart was laboring along now, and I started panting.

Her heart labored like an engine straining to kick over after a night in the cold.

The heart was laboring, the body passing another threshold of shock.