Final answer:
The coronary arteries fill with blood when the aortic valve opens during the cardiac cycle.
Step-by-step explanation:
During the cardiac cycle, the coronary arteries fill with blood when the aortic valve opens. The aortic valve is located between the left ventricle and the aorta. When the left ventricle contracts, it pushes blood out of the heart and into the aorta through the open aortic valve. This allows the coronary arteries to receive blood and supply oxygen to the heart muscle.