The phrase "contraction of the heart" refers to a condition in which the heart muscle contracts abnormally, leading to an irregular and often weakened heartbeat. Full definition
Thyroid hormones stimulate a faster heart rate and a stronger contraction of the heart muscle. (chai-online.org)
I experience the loss of these beloved friends as contractions of the heart that take you over like you're in labor, leaving you barely able to breathe. (mindbodygreen.com)
This is made possible by the more efficient contraction of the heart, pumping more blood through the body. (mypetneedsthat.com)