Contractions push blood on to the next location. Therefore, the sinoatrial node pushes blood from the right atrium to the right ventricle, and from the left atrium to the left ventricle. The atrioventricular node pushes blood from the right ventricle to the pulmonary artery, and from the left ventricle to the aorta. The contraction phase of the heartbeat, when blood is being pushed out, is called the systole . The relaxation phase of the heartbeat, when blood is filling the chambers, is called the diastole .
Arteries push blood away from the heart.
Veins push blood toward the heart. Individual cells are fed by capillaries which connect the arterial and veinous systems. Capillaries are so small only one blood cell can pass through them at a time. Acute and chronic. Chronic conditions have gradual onset of symptoms which may not become severe for years.