As the central pump for blood, the heart provides blood flow to every part of the body – including itself.
When the heart muscle contracts, during the phase known as systole (SIS-tahl-ee), it pushes blood out into the tissues of the body (including the lungs, where it will get oxygenated). At this time, when the heart is working hard to provide for the body, the force of its contraction squeezes its own blood vessels (the coronary arteries), impeding flow to the heart muscle itself. Thus, when the heart is working the hardest, it can't get any blood flow for itself.
When the heart muscle relaxes, during diastole (die-AS-toll-ee), that's when the coronary arteries open and the heart receives its own supply of fresh blood. This rest phase not only allows the chambers of the heart to fill with blood again, ready for pumping; it also gives the heart muscle itself the blood flow that's crucial for it to continue functioning. The rest phase is a necessary part of the cycle.
Sometimes, in our lives, we may feel like we're stuck in systole; constantly working hard to provide for others, without the time for rest. While we're in this mode, we can't get what we need for ourselves. Like the heart, we squeeze down on our own flow of nourishment while we work hard for others. If we stay like this, we often begin to experience burnout, as we continue to try to function on an empty tank, with no fresh flow to sustain us.
Remember that your own nourishment comes when you relax. Like the heart, when you're in diastole, that's when you get your own blood flow. The heart loves to provide for others, pumping nourishment out far and wide. Just remember that the heart itself is nourished during rest.