monkey muscle n.— «The symptoms you describe are most likely the result of a tear in the one of the two heads of the main calf muscle—the gastrocnemius. This is also known as a “torn monkey muscle” injury, for reasons I don’t...
pull a heart muscle v. phr. to withdraw, back out, or retreat from a competition, conflict, or obligation; to chicken out. Editorial Note: To pull a heart muscle is similar to having tiny heart syndrome. (source: Double-Tongued Dictionary)