📝 STANDARD DESCRIPTION:
Heart = 4-chambered muscular pump in the middle mediastinum.
4 chambers: Right atrium → Right ventricle → (lungs) → Left atrium → Left ventricle.
4 Valves:
• Tricuspid (right atrioventricular) — between R atrium & R ventricle.
• Pulmonary semilunar — exit of R ventricle.
• Mitral / Bicuspid (left AV) — between L atrium & L ventricle.
• Aortic semilunar — exit of L ventricle.
3 Layers of Wall:
• Epicardium = visceral pericardium (outer).
• Myocardium = thick cardiac muscle (middle).
• Endocardium = inner endothelial lining.
Pericardium = double-walled fibrous sac:
• Fibrous pericardium (outer).
• Parietal serous pericardium (inner).
• Pericardial cavity has small amount of fluid.
📚 DETAILED DESCRIPTION:
THE HEART — STRUCTURE & POSITION
Position: The heart lies in the middle mediastinum of the thorax, between the lungs. In the ox it occupies the 3rd to 6th intercostal space, with the apex pointing ventrally and slightly to the LEFT of midline (apex sits near the left 5th-6th rib in the lower third of the chest).
SHAPE: Roughly conical — base (broad, dorsal — where vessels enter/exit), apex (pointed, ventral).
FOUR CHAMBERS:
1. Right Atrium (RA) — receives systemic venous blood (cranial vena cava + caudal vena cava + coronary sinus).
2. Right Ventricle (RV) — pumps to lungs via pulmonary trunk.
3. Left Atrium (LA) — receives oxygenated blood from 4 pulmonary veins.
4. Left Ventricle (LV) — pumps to body via aorta. Walls 3× thicker than RV because of higher systemic pressure.
FOUR VALVES (preventing backflow):
• Right AV (Tricuspid) — 3 cusps; held by chordae tendineae attached to papillary muscles of RV.
• Pulmonary semilunar valve — 3 half-moon cusps at base of pulmonary trunk.
• Left AV (Bicuspid / Mitral) — 2 cusps; held by chordae tendineae of LV.
• Aortic semilunar valve — 3 half-moon cusps at root of aorta.
WALL LAYERS:
• Epicardium = visceral layer of serous pericardium.
• Myocardium = cardiac muscle (thick, contractile).
• Endocardium = inner endothelial lining (continuous with vessels).
PERICARDIUM:
• Fibrous pericardium — outer dense CT sac; attaches to sternum via sternopericardiac ligament.
• Parietal serous pericardium — lines inside of fibrous layer.
• Visceral serous pericardium = epicardium — covers heart surface.
• Pericardial cavity — between parietal & visceral layers; small amount of serous fluid.
CONDUCTION SYSTEM: SA node (in RA wall) → AV node → Bundle of His → R + L bundle branches → Purkinje fibres in ventricles.
CORONARY CIRCULATION: First branches of aorta = right + left coronary arteries → supply heart muscle.
SPECIAL: OSSA CORDIS in adult cattle — small bones in fibrous skeleton at aortic root (covered earlier).
// COMPARATIVE ANALYSIS
| OX |
Heart 3rd-6th ICS. Has ossa cordis. Apex on midline at the lower third of left thorax. |
| HORSE |
Massive heart (~5 kg in Thoroughbred, up to 10 kg in racing legends like Secretariat). 4-1-2 chordal arrangement. |
| DOG |
Heart at 3rd-6th ICS. Cardiac silhouette routinely assessed on radiograph (vertebral heart score). |
CLINICAL RELEVANCE
Auscultation Sites (Cow): Left side — Mitral (5th ICS, lower third), Aortic (4th ICS, mid-third), Pulmonic (3rd ICS, mid-third). Right side — Tricuspid (3rd-4th ICS, mid-third). Pericardiocentesis: Aspiration of pericardial fluid in tamponade. Hardware Disease (cattle): Reticular foreign body penetrates pericardium → septic pericarditis ('washing-machine' heart sounds).
