Which factor does NOT contribute to myocardial demand?

Oxygen saturation, while critical for overall oxygen delivery to the myocardium, does not directly contribute to myocardial demand. Myocardial demand is primarily influenced by factors that dictate how hard the heart must work to maintain adequate blood flow and oxygen supply to meet the metabolic needs of the heart muscle itself.

Heart rate is a key determinant of myocardial demand because a higher heart rate increases the frequency of contractions, leading to a greater oxygen requirement. Similarly, ventricular wall stress is part of the equation since it reflects the load against which the heart must pump; greater stresses lead to increased myocardial oxygen demand. Contractility, or the inherent strength of myocardial contraction, also significantly impacts how much oxygen the myocardium requires during each heartbeat.

While oxygen saturation plays an essential role in ensuring that adequate oxygen is available for the heart, it does not affect how much oxygen is needed in terms of workload or performance, which is what constitutes myocardial demand.