Stages

Blood enters the heart

- Diastole (filling phase, lasts approx. 0.4 seconds)
- Relaxation (passive action)

When the cardiac muscle is relaxed the heart fills with blood under low pressure from the veins.
a. Blood flows from the veins into the atria.
b. The cuspid valves open.
c. The atria fill with blood.
d. Blood flows into and fills the ventricles.
e. The right side fills with deoxygenated blood and the left fills with oxygenated.

2. - Systole ( emptying phase approx. 0.4 seconds)
- Contraction

When the cardiac muscle contracts the chambers of the heart empty of blood.
Two stages involved:

Stage 1 (Atrial Systole approx. 0.1 seconds)
a. Atria contract under stimulation from the sino-atrial node (pacemaker)
b. Ventricles are topped up with extra blood from the atria.
c. Delayed arrival of stimulus to the ventricles from the sino-atrial node.

Stage 2 (Ventricular systole approx. 0.3 seconds)
a. The impulse enters the ventricles at the A.V. node (atrio-ventricular node), lies at the bottom of the right atrium against the septum. The impulse travels along the septum and through the ventriculas walls, stimulating contraction..
b. The cuspid calves close, the semi-lunar valves open.
c. Cuspid valves close to prevent backflow to the atria.
d. Once the blood enters the arteries, the semi-lunar valves close preventing backflow into the ventricles.

*A heart murmur is any abnormal sound associated with the heartbeat. A heart murmur may indicate damage to one or more of the valves.

	Created by eimearkelly3 about 8 years ago

	Copied by Amy Rennie about 8 years ago

Note on The Heart And The Blood Vessels, created by Amy Rennie on 10/04/2016.