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06.03 Cardiac Cycle

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  1. Cardiac Cycle
    1. Systole
      1. Contraction
    2. Diastole
      1. Relaxation
    3. Diastasis
      1. Pause between relaxation and contraction
    4. Assumes ventricular, must state atrial if referring to atrial

Nursing Points


  1. Cardiac Cycle
    1. Ventricular diastole and diastasis
      1. Blood from vena cava → right atrium
        1. Tricuspid valve open
      2. Blood flows through open valve to R.V.
      3. Blood from PVs → left atrium
        1. Bicuspid valve open
      4. Blood flows through open valve to LV
      5. During diastasis – Ventricles fill to 70% capacity
    2. Atrial systole
      1. Both atria contract simultaneously
      2. Fill remaining 30% of ventricles with blood
    3. Atrial diastole
      1. Both atria relax during ventricular systole
    4. Ventricular systole
      1. Both ventricles contract
      2. Pressure increases in both ventricles
      3. Bicuspid and tricuspid valves close
        1. Papillary muscles contract to hold valves closed
        2. Prevents backflow to atria
      4. Pulmonic and Aortic valves open
        1. Blood from RV flows through open pulmonic valve into pulmonary artery
        2. Blood from LV flows through open aortic valve into aorta
      5. Small amount remains in ventricles
        1. “End Diastolic Volume” (EDV)
    5. Ventricular diastole
      1. Pulmonic and aortic valves close
        1. Prevents backflow of blood
    6. The cycle repeats
  2. Heart sounds
    1. Normal
      1. S1 or systolic
        1. Long duration
        2. Low pitch
        3. Ventricles contract
        4. AV valves close
      2. S2 or diastolic
        1. Ventricles relax
        2. Semilunar valves close
    2. Abnormal — due to diseased heart valves
      1. Stenosis — edges of valves fuse together so that valve cannot open to its fullest extent -OR- presence of vegetation prevents full opening
        1. Creates a murmur (whoosh sound)
          1. Blood is trying to pass through an opening that is smaller than normal
      2. Regurgitation – valves don’t close completely
        1. Loss of substance of heart valves
        2. Blood regurgitates backwards
          1. RV→ RA
          2. PT → RV
          3. Aorta → LV (2nd most common)
          4. LV → LA (most common)


  1. Refer to Heart Sounds lesson in Cardiac (Med-Surg) course

Betts, J.G., et al. (2017). _Anatomy and physiology_. Houston, TX: OpenStax, Rice University. Retrieved from

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Video Transcript

In this lesson we’re going to talk about the cardiac cycle and how blood is pumped throughout the body

Before we get started I want to go over a couple of really important points. These are some terms that you really need to know. The first one is called systole, which is really just a contraction of whatever chambers of the heart squeezing. You need to know is diastole, which is a relaxation. And then you have something called diastasis, which is the pause between relaxation and control. The other thing that you have to know is that if you want to speak to something specifically about the atria, you have to say atrial before it. So it would be, or atrial diastole. Otherwise it’s considered ventricular.

We were talking about the cardiac cycle we’re going to look at the atria first. This is called ventricular diastole, and the ventricles are relaxing and blood is coming in from the vena cava, so the vena cava and the superior vena cava and it’s filling blood in the right atrium and blood is going from the right atrium to the right ventricle through the tricuspid valve. In the left side you have blood pulling in from the pulmonary veins and they’re going to the left atrium. Then it’s going to go from the left atrium to the left ventricle. Is essentially a pause in here and it’s called diastasis. And what happens is this pause allows the ventricles to fill in 70%. In His Image you can see that the Atria fill and the ventricles are relaxing and there’s a pause before anything squeezes. This is the diastasis that I’m talking about.

Now we get to the point where the Atria relax this is called atrial diastole. And you can see it here

When we talk about atrial systole, we’re talking about that the atria contract. And both the right and left atria are going contract simultaneously. This is going to fill the rest of the 30% of the blood is in the ventricles, and this is called atrial kick

Then finally you get to ventricular systole. So both ventricles are going to contract. This causes an increase in ventricular pressure, because this is where the power house of all the blood exiting the heart happens. The bicuspid and tricuspid valves are going to close to keep backflow from happening. At the same time the papillary muscles here are going to contract to keep help keep those valves closed.

The pulmonic and aortic valves, so the semilunar valves, are going to open, and the blood is going to rush out of the heart and into either the aorta or the ones. A small amount of blood is left in the ventricles, and this is known as end diastolic volume.

So once the blood is out of the ventricles, the pulmonic and aortic valves are going to close and that’s going to prevent backflow from the pulmonary artery and the aorta back into the ventricles. And then the cycle is going to repeat.

So once the blood is out of the ventricles, the pulmonic and aortic valves are going to close and that’s going to prevent backflow from the pulmonary artery and the aorta back into the ventricles. And then the cycle is going to repeat.

Okay so let’s recap.

When were talking about systole and diastole systole is contraction of whatever chamber were talking about and diastole is the relaxation of that chamber.

Diastasis is the pause between systole and diastole, and it allows the ventricles to fill 70% full.

The valves are like open doors in between each chamber. Those valves are going to remain open while the the blood moves from one chamber to another.
When we talked about normal heart sounds were talking about S1 and S2. That’s one comes from the closure of the tricuspid and mitral valve, and S2 comes from a closure of the semilunar valves.

Normal heart sounds come from incomplete closure or opening of those valves, or a narrowing of the valve so that blood is forced through a small opening.

And that’s our lesson on the cardiac cycle. Make sure you check out all the resources attached this lesson. Now go out and be our best selves today, and as always happy nursing..