Which of the following accurately describes the process of coronary circulation?

A. Myocardium:
The myocardium is the muscular layer of the heart, not part of the pericardium.

B. Fibrous pericardium:
The fibrous pericardium is the outer tough layer that anchors the heart in the thorax; it is not directly attached to the heart muscle.

C. Serous pericardium (visceral layer):
The visceral layer of the serous pericardium, also called the epicardium, lies directly on the heart muscle, providing lubrication and a smooth interface between the heart and the pericardial cavity.

D. Parietal pericardium:
The parietal layer lines the inner surface of the fibrous pericardium but is separated from the myocardium by the pericardial cavity.

A. S1:
S1 is produced by the closure of the mitral and tricuspid valves at the beginning of systole. It signals the start of ventricular contraction and is best heard at the apex for the mitral valve and lower left sternal border for the tricuspid valve.

B. S4:
S4 occurs during atrial contraction in late diastole and may indicate a stiff or hypertrophic ventricle; it is not related to AV valve closure.

C. S2:
S2 occurs with the closure of semilunar valves (aortic and pulmonic) at the end of systole, marking the beginning of diastole.

D. S3:
S3 occurs during rapid ventricular filling in early diastole and may indicate volume overload; it does not correspond to AV valve closure.