mall but sharp rise in atrial pressure. When the semilunar valves open, the phase of ventricular ejection begins. Ejection is initially rapid, but slows down as systole progresses. The intraventricular pressure rises to a maximum and then declines somewhat before ventricular systole ends. Late in systole, the aortic pressure is actually higher than the ventricular pressure, but for a short period, momentum keeps the blood moving forward. The AV valves are pulled down by the contractions of the ventricular muscle, and the atrial pressure drops.5 In early diastole, after the ventricular muscle if fully contracted, the already falling ventricular pressure drops even more rapidly. This is the period known as protodiastole and it lasts about 0.04 seconds. It ends when the momentum of the ejected blood is overcome and the semilunar valves close. After the valves are closed, pressure continues to drop rapidly during the period of isovolumetric relaxation. Isovolumetric relaxation ends when the ventricular pressure falls below the atrial pressure and the AV valves open, thus allowing the ventricles to fill. Again, filling is rapid at first, then slows as the next cardiac contraction approaches. Atrial pressure continues to rise after the end of ventricular systole until the AV valves open, upon which time it drops and slowly rises again until the next atrial systole.6,2,&4Summary: The heart is arguably the most vital organ the human body possesses. Without the heart, none of the tissues in the body would receive the vital oxygen necessary for them to maintain survival. Heart disease is the number one killer of people in America today. Due to this disturbing fact, it is no wonder such a large percentage of the fellowships granted by the National Institutes of Health go towards heart related illnesses....
