The Cardiac CycleThe heart is a very important organ in the human body . It causes the flow of blood, which is essential to life and if there is even a minor problem in the heart, there can be severe repercussions for the patient.

There are also some subtle differences between the valves. The atrioventricular valves both have fibrous strands during ventricular systole, the papillary muscles contract . This does not happen in semilunar valves .

The heart and its efficient structure allows it to be instrumental in the circulatory system . Humans have a double circulatory system ,this means that the blood goes through the heart twice as it goes around the body. This allows the heart to pump deoxygenated blood to the lungs and oxygenated blood to the rest of the body. Deoxygenated blood returns to the heart through the inferior and superior vena into the right atrium . Blood flows into the right ventricle through the tricuspid valve. The blood then enters the pulmonary artery, and backflow is prevented by the semilunar pulmonic valve. Blood then returns to the heart from the lungs after being oxygenated via the pulmonary veins and enters the left atrium. The blood flows through the mitral valve (AV valve) into the left ventricle. Blood is then released into the aorta where it then goes to the rest of the body.

Each time a human heart beats , a Cardiac cycle occurs. When the cardiac muscle contracts, the pressure increases and volume decreases. On average, the muscle contracts 75 times per minute and pumps 75 cm squared of blood from the ventricle during each beat. The one thing about cardiac muscle that is extraordinary is that it is myogenic , and it can contract on its own , automatically, even when the human being is sleeping, walking or even in a coma. In the cardiac cycle, the atria receive blood from the veins, and store it prior to a heartbeat. Both atria contract and stored blood is pushed across the atrioventricular valves into the ventricles. After both atria contract, atrial systole, both ventricles contract. This is known as ventricular dystole, and the pressure in ventricles increases, the valves close to prevent backflow and volume decreases. This ventricle systole causes blood to go into the arteries. After this happens , ventricular diastole occurs. This involves in the chambers relaxing, and the volume to increase for the cycle to start again.

The cardiac cycle causes the noises made by the heart. The lub dupp sound made by the heart is when the ventricles systole (contract) , and causes the lub whereas the dupp is caused by the semilunar valves closing.

The heart is a fascinating organ, and the circulatory system is one of the most important systems, which allows life to carry on and humans to respire . The cardiac cycle and the heart beating allow blood to be pumped around the body and for fresh oxygen to be supplied to the body, as well as the removal of carbon dioxide.