What does diastole refer to in the cardiac cycle?

Diastole refers to the period in the cardiac cycle when the heart muscle relaxes, allowing the chambers of the heart, primarily the ventricles, to fill with blood. During this phase, the pressure within the heart decreases, creating a vacuum that helps draw blood into the atria from the veins. This filling phase is critical for ensuring that there is an adequate volume of blood available to be pumped out during the subsequent contraction phase, known as systole. Understanding diastole is essential, as it directly relates to the heart's ability to supply the body's tissues with oxygenated blood and nutrients.

The other options highlight aspects of the cardiac cycle but do not describe diastole accurately. While contraction and blood ejection are part of systole, the phase of highest arterial pressure occurs during that same contraction phase, emphasizing the difference in cardiac processes.