Cardiac activity is controlled by several mechanisms that influence the heart’s rate and force of contraction.

A. Nodal tissue – The sino‑atrial (SA) node and atrioventricular (AV) node are specialized myocardial cells that generate and transmit the electrical impulses which set the rhythm of the heart. These pacemaker tissues are the primary intrinsic regulators of cardiac activity.

B. A special neural centre in the medulla oblongata – The cardiovascular centre located in the medulla receives input from baroreceptors and chemoreceptors and modulates autonomic outflow. Through sympathetic and parasympathetic pathways it can increase or decrease heart rate and contractility.

C. Adrenal medullary hormones – The adrenal medulla releases catecholamines (epinephrine and norepinephrine) into the bloodstream during stress or exercise. These hormones bind to β‑adrenergic receptors on the heart, enhancing heart rate and contractile strength.

D. Adrenal cortical hormones – The cortex primarily secretes mineralocorticoids (aldosterone) and glucocorticoids (cortisol), which regulate electrolyte balance and metabolism. They do not exert a direct, rapid influence on cardiac rhythm or contractility.

Since the nodal tissue, medullary centre, and adrenal medullary hormones all play direct roles in regulating heart function, while adrenal cortical hormones do not, the correct combination of regulators is A, B and C only.