RCIS Practice Test 2026 – All-in-One Exam Prep

The coronary arteries primarily receive blood flow during diastole, which is the phase of the cardiac cycle when the heart muscle relaxes after contraction. During diastole, the pressure in the heart chambers decreases, allowing the coronary arteries to fill with oxygen-rich blood. This is critical because the heart muscle requires a constant supply of oxygen and nutrients, which is delivered through these arteries.

In contrast, during systole, which is the contraction phase of the heart, the muscle itself is actively contracting and putting pressure on the coronary arteries, which limits blood flow. Therefore, while the heart is working hard to pump blood during systole, the need for oxygen in the heart tissue increases, but the supply is restricted due to the compression of the arteries.

Understanding the timing of coronary perfusion during the cardiac cycle is essential for grasping how the heart sustains itself during various states of activity and rest.