1. The heart is made of muscle and has four chambers, two on each side. The left side contains oxygenated deoxygenated blood and the right side contains oxygenated deoxygenated blood.

2. The TWO atria are the larger, less muscular smaller, less muscular smaller, more muscular larger, more muscular upper chambers lower chambers .

3. The TWO ventricles are the larger, more muscular smaller, less muscular larger, less muscular smaller, more muscular upper chambers lower chambers .

4. The left ventricle is more muscular than the right less muscular than the right since it has to pump blood only around the lungs around the whole body around the whole body and the lungs

How blood moves through the heart.

1. Deoxygenated blood from the lungs body enters the left atrium right atrium left ventricle right ventricle which then contracts.

2. This forces blood into the left atrium right atrium left ventricle right ventricle which then contracts. This forces blood out of the heart into the vein leading to the lungs artery leading to the lungs vein leading to the body artery leading to the body .

1. Oxygenated blood from the lungs body enters the left atrium right atrium left ventricle right ventricle which then contracts.

2. This forces blood into the left atrium right atrium left ventricle right ventricle which then contracts. This forces blood out of the heart into the vein leading to the lungs artery leading to the lungs vein leading to the body artery leading to the body .

The different Blood Vessels

1. Arteries carry blood away from towards the heart and veins carry blood away from towards the heart.

2. Arteries have thicker walls and a larger lumen thinner walls and a larger lumen thicker walls and a smaller lumen thinner walls and a smaller lumen than veins. They also have no valves valves and contain less elastic and muscle fibres more elastic and muscle fibres .

3. All arteries carry oxygenated deoxygented blood except the one from the lungs one to the lungs .

4. Capillaries are microscopic and only one cell thick. They have valves and link arteries to veins no valves and link arteries to veins valves and link arteries to the heart no valves and link veins to the heart .