**Core Concept**
Myocardial contractility refers to the intrinsic ability of the heart muscle to generate force and velocity of contraction. It is influenced by various factors, including the concentration of calcium ions, the activity of the sarcoplasmic reticulum, and the sensitivity of the contractile apparatus.

**Why the Correct Answer is Right**
Increased myocardial contractility can occur through various mechanisms, including the administration of positive inotropic agents. These agents work by increasing the concentration of calcium ions within the cardiac myocytes, thereby enhancing the contractile force. For example, catecholamines such as epinephrine and norepinephrine increase contractility by stimulating beta-adrenergic receptors, which activate the Gs protein and increase the activity of adenylyl cyclase, leading to an increase in cyclic AMP and ultimately, an increase in calcium ion release from the sarcoplasmic reticulum.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not increase myocardial contractility. In fact, certain anesthetics can decrease contractility by reducing the sensitivity of the contractile apparatus to calcium ions.
**Option B:** This option is incorrect as it is a negative inotropic agent, which decreases myocardial contractility. Beta-blockers, such as propranolol, reduce contractility by blocking the action of catecholamines on beta-adrenergic receptors.
**Option C:** This option is incorrect as it is a negative inotropic agent that can decrease myocardial contractility. Angiotensin II has a biphasic effect on contractility, but at low doses, it can decrease contractility by reducing the activity of the sarcoplasmic reticulum.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that increased myocardial contractility can be beneficial in certain clinical scenarios, such as heart failure, but it can also increase the oxygen demand of the heart, potentially leading to ischemia or arrhythmias.

**Correct Answer:** D.