**Core Concept**
Cardiac output (CO) is the volume of blood the heart pumps per minute. It is a critical parameter in assessing cardiac function and is influenced by factors that affect the heart's ability to pump blood and the vascular system's ability to accommodate the blood volume.

**Why the Correct Answer is Right**
Cardiac output is determined by the product of heart rate (HR) and stroke volume (SV). This relationship is described by the formula: CO = HR x SV. Heart rate is the number of contractions of the heart per minute, while stroke volume is the volume of blood pumped by the left ventricle with each beat. The correct answer is **stroke volume** because it directly affects the amount of blood pumped by the heart per minute.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the determination of cardiac output. While blood pressure is related to cardiac output, it is not a direct determinant.
* **Option B:** This option is incorrect because cardiac output is not determined by peripheral resistance alone. While peripheral resistance can affect stroke volume, it is not the primary factor in determining cardiac output.
* **Option D:** This option is not a direct determinant of cardiac output. While vasopressors can increase peripheral resistance and subsequently affect cardiac output, they are not the primary factor in determining cardiac output.

**Clinical Pearl / High-Yield Fact**
In clinical practice, cardiac output can be estimated using various formulas, including the Fick principle and thermodilution. Understanding the relationship between heart rate, stroke volume, and cardiac output is crucial in managing patients with cardiovascular diseases.

**Correct Answer: C. Stroke volume**