MRCS Part B Revision · Anatomy
Heart 3 — MRCS Part B Anatomy
By Dr Richard Miller, MBChB FRCS · Reviewed
Heart 3 is a surgical anatomy station. Three of the seventeen examined stations in the MRCS Part B OSCE are surgical anatomy. The anatomy stations put a prosected specimen, a model or an image in front of you and ask you to identify structures and say what they do, what they relate to and what happens when they are injured.
What you need to know for the Heart 3 station
The heart with its coronary arteries and veins displayed. The questions are the origin and course of each artery, dominance, and the supply of the nodes, because these decide what an occlusion does.
Right coronary artery
Arises from the right (anterior) aortic sinus, passes forward between the pulmonary trunk and the right auricle, and runs in the right atrioventricular groove around the inferior border to the back of the heart. Branches, in order: the conus artery and the sinoatrial nodal artery near its origin, right atrial and ventricular branches, the right marginal artery along the inferior border, and at the crux the posterior interventricular (posterior descending) artery, which runs to the apex, and the atrioventricular nodal artery. Occlusion gives an inferior infarct, with bradycardia and heart block from the nodal branches.
Left coronary artery
Arises from the left (posterior) aortic sinus, runs a short course behind the pulmonary trunk and under the left auricle, and divides into the left anterior descending artery, which runs down the anterior interventricular groove to the apex giving diagonal and septal branches, and the circumflex artery, which runs in the left atrioventricular groove around to the back giving the left marginal artery. The anterior descending supplies the anterior wall, the apex and the front two-thirds of the septum with the bundle branches inside it, which is why its occlusion is the largest infarct and the one that causes bundle branch block and septal rupture.
Dominance
The dominant artery is the one that gives the posterior interventricular artery. In about 85% of people it is the right, in around 8% the left circumflex, and the rest are co-dominant. In a left-dominant heart the circumflex also supplies the atrioventricular node and much of the inferior wall, so a circumflex occlusion is far more dangerous.
The nodes
The sinoatrial node is supplied by the right coronary artery in about 60% of people and by the circumflex in the rest. The atrioventricular node is supplied by the dominant artery, so by the right in about 90%. Both nodes have some collateral supply, which is why complete heart block after an inferior infarct often recovers.
Venous drainage
Most of the heart drains to the coronary sinus, which lies in the posterior atrioventricular groove and opens into the right atrium between the inferior vena cava and the tricuspid valve, guarded by the Thebesian valve. It receives the great cardiac vein from the anterior interventricular groove, the middle cardiac vein from the posterior interventricular groove, the small cardiac vein from the right margin, the posterior vein of the left ventricle and the oblique vein of the left atrium (of Marshall). The anterior cardiac veins from the right ventricle open straight into the right atrium, and the venae cordis minimae (Thebesian veins) drain from the wall directly into all four chambers.
Images from this station
What are you asked at the Heart 3 station?
The station runs to 13 questions over nine minutes. These are the questions as they are put to you; the model answers are in the question bank.
- Identify structures 1-4
- Identify areas 5 and 6
- Identify structures 7-9
- Identify structures 10 and 11
- Identify structures 12 and 13
- Identify structures 14 and 15
- Identify structures 16-17
- Describe the origin and course of the right coronary artery
- Describe the origin and course of the left coronary artery
- What are the branches of the right coronary artery?
- What is 'left dominance'?
- What is the blood supply of the SA and AV nodes?
And 1 more at this station.
How is the anatomy station marked in MRCS Part B?
An anatomy station is marked out of 20, and all 20 marks go to clinical knowledge and its application. No communication, technical-skill or professionalism marks are available in an anatomy bay, which is unusual: in most other stations more than half the marks sit outside your factual knowledge.
FAQ
What does the Heart 3 station ask?
It opens with "Identify structures 1-4" and runs to 13 questions over nine minutes. An anatomy station is marked out of 20, and all 20 marks go to clinical knowledge and its application. No communication, technical-skill or professionalism marks are available in an anatomy bay, which is unusual: in most other stations more than half the marks sit outside your factual knowledge.
How many anatomy stations are there in MRCS Part B?
Three of the seventeen examined stations are surgical anatomy, and two more are surgical pathology. Together they make up the five Anatomy and surgical pathology stations of the Applied Knowledge component.
How are the anatomy stations marked?
Each station is marked out of 20 and all 20 marks are awarded for clinical knowledge and its application. You also receive a separate global rating of pass, borderline or fail for the station.
Are the specimens real?
Yes. Anatomy bays use prosected cadaveric specimens, models and images. Candidates report being shown photographs of specimens as well as the specimens themselves, so practise on real dissection photography rather than diagrams alone.
What happens if I get an early question wrong?
The intercollegiate guidance says that if a wrong answer would affect your performance on later questions at the same station, the examiner gives you the correct answer before moving on. One mistake does not have to cost you the whole bay.
How many stations are in the MRCS Part B OSCE?
Seventeen examined stations of nine minutes each, with a minute to read the task before each one. Two preparation stations and at least one rest station bring the circuit to about twenty, and the exam takes about three and a half hours.
What is the pass mark for MRCS Part B?
There is no published pass mark. The cut score is set separately for Applied Knowledge and Applied Skills, for each circuit, by borderline regression. Published pass rates across the 2024/25 diets ranged from 51% to 66%.
Can I fail a station and still pass?
Yes. There is no rule about how many stations you may fail: the cut score applies to your total mark in each component, so a weak station costs the marks you lost on it and strong stations elsewhere can make them back. Applied Knowledge and Applied Skills are passed separately and must both be passed at the same sitting, so a strong anatomy performance cannot rescue a weak communication one.
Dr Richard Miller, MBChB FRCS
Station summaries are reviewed against the current intercollegiate MRCS syllabus and the published marking blueprint. Guidance changes between diets: check the royal colleges' own pages before relying on a date, a fee or a threshold.
Practise this station
The question bank carries the model answer to every question above, with the rest of the anatomy stations.
More anatomy stations