**Core Concept**
The oxygen consumption of the heart is a critical parameter that determines the myocardial oxygen demand. It is primarily influenced by the contractile force and the rate of contraction of the cardiac muscle. The heart's oxygen consumption is closely linked to its metabolic activity and the energy requirements for pumping blood.

**Why the Correct Answer is Right**
The correct answer is related to the contractile force and rate of contraction of the cardiac muscle. The heart's oxygen consumption is directly proportional to the force of contraction and the frequency of contractions. This is because the cardiac muscle requires more energy to generate force and contract at a faster rate. The contractile force is influenced by the intracellular concentration of calcium ions, which in turn is regulated by the activity of the calcium channels and the sarcoplasmic reticulum. The rate of contraction is influenced by the autonomic nervous system, particularly the sympathetic nervous system, which increases the heart rate and contractility.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the heart's oxygen consumption is not primarily influenced by the cardiac output. While cardiac output is an important determinant of the heart's workload, it is not the primary factor that determines oxygen consumption.

**Option B:** This option is incorrect because the heart's oxygen consumption is not primarily influenced by the arterial oxygen tension. While changes in arterial oxygen tension can affect the heart's oxygen consumption, it is not the primary determinant.

**Option C:** This option is incorrect because the heart's oxygen consumption is not primarily influenced by the venous oxygen tension. While changes in venous oxygen tension can affect the heart's oxygen consumption, it is not the primary determinant.

**Clinical Pearl / High-Yield Fact**
The heart's oxygen consumption is directly proportional to the force of contraction and the frequency of contractions. This is an important principle to remember when assessing patients with cardiac disease, as it can help guide treatment decisions and predict the risk of myocardial ischemia.

**Correct Answer:** C. Contractile force and rate of contraction