foreign Loops are graphs where the pressure inside the left ventricle is on the y-axis and the volume of the left ventricle is on the x-axis each Loop represents one cardiac cycle including both ventricular systole and diastole or more simply one heartbeat alright let's start at the lower right hand corner This is the End diastolic point and it's the point in the cardiac cycle when diastole is over the mitral valve or the communicating door between the left atrium and the left ventricle has just closed and as it closed it made a long loud sound kind of like a [Music] that's known as the first heart sound or S1 so at this point the left ventricle is filled with a maximum volume of blood known as the end diastolic volume which is normally about 120 milliliters you can imagine The ventricle as a relaxed sack of muscle that's full of blood so the pressure is low after that the left ventricle contracts and that marks the beginning of systole this makes the pressure shoot up but since both mitral and aortic valves are closed blood can neither enter nor leave The ventricle so the volume doesn't change this phase is called isovolumetric contraction and it lasts for about 0.05 seconds eventually the pressure inside the left ventricle reaches approximately 75 millimeters of mercury becoming just higher than the pressure inside the aorta forcing the aortic valve to pop open this pressure reflects the pressure in the aorta right at the beginning of the ejection phase or the lowest that the blood pressure in the aorta is going to be and it's known as the diastolic blood pressure or DBP for short okay now once the ejection phase starts it lasts for about 0.25 seconds that's when blood is ejected out of the left ventricle and into the aorta decreasing left ventricular volume the left ventricle continues to contract so ventricular pressure keeps Rising further meanwhile blood is rushing through the aorta so its pressure increases as well in fact during this phase left ventricular and aortic pressures are essentially equal this goes on until they reach a peak of about 120 millimeters of mercury known as systolic blood pressure or spp before finally starting to come down again the difference between systolic and diastolic blood pressures in this case 120 minus 75 equals 45 millimeters of mercury and this is called pulse pressure because it reflects the throbbing pulsation felt in an artery during systole eventually aortic pressure exceeds the pressure within the left ventricle so the aortic valve snaps shut as it does this it makes a sharp sharp sound kind of like a [Music] and this is called the second heart sounds or S2 so this marks the end of the systolic period also known as an systolic point at this point the volume inside the left ventricle known as the interstolic volume is normally about 50 milliliters if we calculate the difference between the end diastolic volume and the N systolic volume we'll get the stroke volume which is the volume of blood the left ventricle ejects or simply squeezes away on every heartbeat or stroke during this ejection period in this case 120 minus 50 is a stroke volume of 70 milliliters stroke volume is a useful measurement but it can vary based on the size of the person's heart so another helpful measurement is the ejection fraction which is the stroke volume divided by the end diastolic volume in this example it's 70 divided by 120 which is about 58 percent in other words 58 of the blood volume in the left ventricle gets pumped out during each heartbeat once the aortic valve has closed the ventricular muscle starts relaxing so pressure within the ventricle Falls however all valves are closed so the volume remains consistent this is the isovolumetric relaxation phase and it lasts for about 0.15 seconds eventually the pressure drops below the left atrial pressure and that allows the mitral valve to open due to the pressure gradient blood from the atrium flows into the ventricle at the beginning passively and at the end with an extra push due to the atrial contraction as the left ventricle fills with blood its volume comes back up to 120 milliliters or its end diastolic volume while its pressure increases only slightly actually this relaxation phase goes on for kind of a long time period compared to the previous phases about 0.55 seconds until there's no more pressure gradient between the two heart chambers and the mitral valve closes letting the cycle start all over again all this happens during one heartbeat and with every heartbeat or stroke the heart is doing work and that's called stroke work and it's proportional to the area inside the loop in other words the bigger the loop and the more area inside of it the more stroke work our heart does alright as a quick recap pressure volume Loops are graph showing the changing relationship between the left ventricular pressure and the left ventricular volume during a cardiac cycle pressure volume Loops can provide us with useful information such as stroke volume or end diastolic volume as well as systolic diastolic and pulse pressure helping current and future clinicians Focus learn retain and Thrive learn more