Blood Flow Through the Heart

• Blood flow through the heart follows a specific sequence, ensuring efficient oxygenation and circulation throughout the body. 
• The heart consists of four chambers: the right atrium, right ventricle, left atrium, and left ventricle.
• There are also four major valves as well: the tricuspid, pulmonary, mitral, and aortic valves

Deoxygenated Blood Entry

• Deoxygenated blood enters the right atrium via the superior vena cava (from the upper body) and the inferior vena cava (from the lower body).
• The coronary sinus also empties deoxygenated blood from the heart muscle itself into the right atrium.

Right Atrium to Right Ventricle

• The blood flows from the right atrium into the right ventricle through the tricuspid valve (also known as the right atrioventricular valve).
• The tricuspid valve prevents backflow of blood from the right ventricle into the right atrium.

Right Ventricle to Pulmonary Artery

• The right ventricle contracts and pumps the deoxygenated blood through the pulmonary valve into the pulmonary artery.
• The pulmonary valve (or pulmonic valve) prevents backflow of blood from the pulmonary artery back into the right ventricle.
• The pulmonary artery is the only artery in the body that carries deoxygenated blood.

To the Lungs

• The pulmonary artery branches into the left and right pulmonary arteries, which carry blood to the left and right lungs, respectively.
• In the lungs, carbon dioxide is exchanged for oxygen in the capillaries surrounding the alveoli.

Oxygenated Blood Entry

• Oxygenated blood returns to the heart via the pulmonary veins, which empty into the left atrium.
• The pulmonary veins are the only veins in the body that carry oxygenated blood.

Left Atrium to Left Ventricle

• The oxygenated blood flows from the left atrium into the left ventricle through the mitral valve (also known as the bicuspid valve or left atrioventricular valve).
• The mitral valve prevents backflow of blood from the left ventricle into the left atrium.

Left Ventricle to Aorta

• The left ventricle, the strongest chamber of the heart, contracts to pump the oxygenated blood through the aortic valve into the aorta.
• The aortic valve prevents backflow of blood from the aorta back into the left ventricle.

To the Body

• The aorta is the largest artery in the body and carries oxygenated blood to all parts of the body (systemic circulation).
• Blood travels from the aorta into smaller arteries, then into arterioles, and finally into capillaries, where oxygen and nutrients are exchanged for carbon dioxide and waste products.
• The deoxygenated blood then returns to the heart through venules and veins, completing the cycle.

Valves

• The heart valves ensure unidirectional blood flow, opening and closing in response to pressure changes within the heart chambers.
• Atrioventricular Valves (Tricuspid and Mitral): These valves prevent backflow from the ventricles into the atria during ventricular contraction (systole).
• Semilunar Valves (Pulmonary and Aortic): These valves prevent backflow from the arteries (pulmonary artery and aorta) into the ventricles during ventricular relaxation (diastole).

Pressure Changes

• The cardiac cycle is driven by pressure changes in the heart chambers.
• Blood flows from areas of high pressure to areas of low pressure.
• Atrial contraction increases atrial pressure, pushing blood into the ventricles.
• Ventricular contraction increases ventricular pressure which closes the AV valves and forces blood through the semilunar valves into the pulmonary artery and aorta.
• Ventricular relaxation decreases ventricular pressure which closes the semilunar valves and allows the AV valves to open and the atria to fill passively.

Summary of Flow

• Deoxygenated blood → right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary artery → lungs → pulmonary veins → left atrium → mitral valve → left ventricle → aortic valve → aorta → body.