An implanted cardiac resynchronization device (ICR) is a medical device used in cardiac resynchronization therapy (CRT). It resynchronizes the contractions of the heart’s ventricles by sending tiny electrical impulses to the heart muscle, which can help the heart pump blood throughout the body more efficiently. CRT defibrillators (CRT-D) also incorporate additional lifesaving therapy to quickly terminate an abnormally fast, life-threatening heart rhythm. CRT and CRT-D have become increasingly important therapeutic options for patients with moderate and severe heart failure.