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Assume you are 45 minutes on the supine position. Furthermore: you stand all of a sudden and fast and without sympaticus activity. The venous return (smooth musculature of vessels) accommodates faster to the change (decrease of venous return) so returns blood to the heart before the sympaticus has accommodated for increased cardiac output. This creates a significant increase in the blood volume entering the heart. In pathological situation where systemic vasoconstriction not occurring normally, the heart is not capable of handling the overdistension; resulting in a pain during the second cardiac cycle.

I am interested in knowing which phase the heart is most vulnerable:

  • filling,
  • isovolumetric contraction
  • ejection
  • isovelumetric relaxation

or more explicitly (from my answer here)

  • Atrial systole
  • Isovolumetric ventricular contraction
  • Rapid ventricular ejection
  • Reduced ventricular ejection
  • Isovolumetric ventricular relaxation
  • Rapid ventricular filling

I think filling can happen normally, but not with the sudden isovolumetric contraction (most sympathetic innervations here, so therefore I think this is the weak link). When there is too much blood in the ventricles, some of the blood is reflected back from the ventricles into the atria causing a painful sensation and possibly tachycardia (as well as an possible increased risk of atrial fibrillation if such events happen regularly).

Is the isovolumetric contraction (systole of ventricles) of the cardiac cycle the possible weak link in accommodating a sudden increased venous return?

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When you stand up suddenly from a supine position, venous return to the heart will decrease, not increase. Moreover, heart chambers overdistension does not cause pain. What will happen when standing up is that systemic vasoconstriction will occur to maintain blood pressure until the venous return can be adjusted. –  Raoul Sep 5 at 1:15
    
@Raoul I agree with every sentence of your comment. I used little bit overloading in my language. I made it now more explicit. However, my case is a pathological situation where the musculature is not able to accommodate and thus causing a pain. –  Masi Sep 5 at 12:29
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If you get retrosternal pain, it means myocardial ischemia is occurring, for whatever reason. I do not think ventricle overloading or blood regurgitation per se can cause pain. –  Raoul Sep 5 at 12:34
    
@Raoul You are right again. I added my explanation and answer about the case here. I think prolonged undiagnosed celiac disease can cause symptoms that remind those of retrosternal pain. –  Masi Sep 5 at 12:41

1 Answer 1

Raoul's gives sensible comments:

  • ventricle overloading not sensible
  • retrosternal pain $\to$ myocardial ischemia
  • other cause reminding retrosternal pain such as celiac disease:

Another possibility is misdiagnosed symptom of the patient. If I remember correctly, the right answer here was that the patient had undiagnosed celiac disease which caused pains reminding those of retrosternal pain. So correct procedures of propedeutics should have been used - I think some way of pressing. The thing was that the student did not know that the patient had celiac disease.

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