Dobutamine affects myocardial performance in all of the following ways EXCEPT:

Dobutamine is a medication commonly used in echocardiography to assess myocardial performance, particularly in patients with heart failure or low cardiac output. Its primary effects include increasing heart rate, enhancing contractility, and reducing vascular resistance, which collectively improve cardiac output.

When evaluating myocardial perfusion specifically, it is essential to understand that increasing heart rate can sometimes lead to a decrease in diastolic filling time, and while dobutamine can enhance blood flow to the myocardium by improving cardiac output, its direct effect on increasing myocardial perfusion is not straightforward.

In particular, while increased contractility (the force of heart muscle contraction) improves the heart's pumping ability, and decreased vascular resistance helps with blood flow, the relationship between dobutamine administration and myocardial perfusion is complex. Therefore, while dobutamine can lead to better overall myocardial oxygen delivery through improved cardiac output, stating that it increases myocardial perfusion might not be an accurate reflection of its primary actions, making this the exception in the options provided.