End diastolic volume increases in:
**Core Concept**
The end diastolic volume (EDV) is the amount of blood present in the ventricles at the end of diastole, just before the start of systole. It is an important indicator of cardiac preload and can be influenced by various factors such as heart rate, contractility, and peripheral resistance.
**Why the Correct Answer is Right**
The correct answer is related to the Starling mechanism, which states that the force of contraction of the heart muscle is directly proportional to the initial length of the cardiac fibers at the onset of contraction. When the EDV increases, the cardiac fibers are stretched, leading to an increase in the force of contraction and an increase in stroke volume (SV). This is because the increased EDV results in a greater amount of blood being available for contraction, leading to a greater stroke volume.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because a decrease in EDV would actually result in a decrease in stroke volume due to decreased preload.
* **Option B:** This option is incorrect because a decrease in contractility would result in a decrease in stroke volume, not an increase.
* **Option C:** This option is incorrect because an increase in peripheral resistance would result in a decrease in stroke volume due to increased afterload.
**Clinical Pearl / High-Yield Fact**
One important clinical correlation is that an increase in EDV can be seen in conditions such as heart failure with preserved ejection fraction (HFpEF), where the heart is unable to relax properly, leading to an increase in EDV.
**Correct Answer: C. Increased venous return.**