Cardiac activities of the heart are regulated by:

The correct option is Nodal tissue.

Step-by-step Explanation:

1. Understanding Cardiac Regulation: The human heart is myogenic, meaning its normal activities are regulated intrinsically by specialized muscles called nodal tissue (such as the sinoatrial node or SA node, and the atrioventricular node or AV node). This nodal tissue can generate action potentials auto-rhythmically without external nervous stimulation.

2. Analyzing the Options:
- Nodal tissue: This acts as the primary intrinsic regulator (pacemaker) of the heart's normal rhythmic activities.
- Special neural centre in the medulla oblongata: While a neural centre in the medulla oblongata can moderate cardiac function through the autonomic nervous system (ANS) to increase or decrease heart rate, it is responsible for the extrinsic regulation, not the fundamental generation of cardiac activities.
- Adrenal medullary hormones: Hormones like adrenaline and noradrenaline can increase cardiac output under stress conditions, representing hormonal regulation.
- Adrenal cortical hormones: These hormones (like aldosterone and cortisol) do not directly regulate the immediate cardiac activities of the heart.

3. Conclusion: Since the heart is myogenic, its basic cardiac activities are primarily initiated and intrinsically regulated by the auto-excitable nodal tissue.