Certified Rhythm Analysis Technician (CRAT) Practice Exam 2025 – All-in-One Study Guide for Exam Success!

The phase of the cardiac cycle characterized by the relaxation of the heart muscle is diastole. During diastole, the chambers of the heart fill with blood. This phase follows systole, which is when the heart contracts to pump blood out to the lungs and the rest of the body.

During diastole, the heart muscle relaxes, allowing the pressure within the heart to decrease, and blood flows from the atria into the ventricles. This is crucial for maintaining the heart's ability to pump blood effectively. The filling of the heart during diastole is essential for ensuring that there is enough blood available for the next contraction during systole.

On the other hand, cardiac output refers to the volume of blood the heart pumps per minute and is not a specific phase of the cardiac cycle. The QRS complex is part of an electrocardiogram and represents the electrical depolarization leading to ventricular contraction, which occurs during systole. Thus, diastole is distinctively recognized as the relaxation phase of the cardiac cycle, allowing the heart to prepare for its next contraction.