The heart muscles cannot contract by themselves so they

The heart muscles cannot contract by themselves so they cardiac cycle works with the heart to create the perfect rhythm. The specialised muscle where the cardiac cycle is initiated is found in the right atrium, which is called the sino-atrial node (SAN), next to the opening of the vena cava. The impulse from the SAN is picked up by the atrio-ventricular node (AVN) and is then passed to a bundle of dense fibres (bundle of His).  The bundle then divides into both the right and left branches which go further into the ventricle walls. These bundles cause the stimulation of the contractions of both ventricles that start in the heart apex and move upwards.  In Bianca’s chart it is shown that her pressure changes in her heart are normal. This is because her Aorta and ventricles contract and relax at the normal pace.  Atrial systole and diastole The contraction of atria comes after the electrical change ( P wave in the ECG). This is because the muscles in the atrial contract towards the atrioventricular septum, then pressure will rise from within the atria and blood is pumped into both ventricles through the open valves. At the beginning of atrial systole, ventricles are filled between 70-80% because there is an inflow during the diastole. The last 20-30% fills during the atrial contraction. The atrial systole movement lasts around 100 milliseconds and ends before ventricular systole because the muscle goes back to diastole.   Ventricular volume The volume rises up as the atria contracts and both ventricles fill up with blood, before dropping suddenly because the blood is forced out into the aorta when the valve opens. This is continuous therefore the volume will increase again as both ventricles fill with blood. Ventricular pressure The pressure is low at first but slowly increases as both ventricles fill up with blood at the same time the atria contracts. The atrioventricular valves on the left close and the pressure rises drastically as the muscular walls contract in the ventricle. As the pressure rises above the pressure in the aorta, the blood forces through into the aorta. The pressure then falls as the ventricles empty out and the walls relax.  An electrocardiogram is a graph that shows the pattern of each electric signal from the heart. IT includes three waves; The P wave is the wave that spreads over the atria from the sino-atrial node, The ORS complex is the wave that passes through the ventricles and the T wave is the wave is the electrical recovery of the ventricles towards the end of the ventricular systole. 


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