MRCS Part B Revision · Anatomy
Heart 2 — MRCS Part B Anatomy
By Dr Richard Miller, MBChB FRCS · Reviewed
Heart 2 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 2 station
The heart opened to show its chambers and valves, with the conducting system and the development of the atrial septum as the two things the specimen cannot show.
Development of the atrial septum
The septum primum grows down from the roof of the common atrium towards the endocardial cushions, leaving the ostium primum below it. Before that closes, the septum primum breaks down at the top to form the ostium secundum. A second, thicker septum secundum then grows down on the right side of the first, overlapping the ostium secundum but stopping short to leave the foramen ovale. The flap of septum primum acts as a valve, letting right-to-left flow through in fetal life. After birth, the rise in left atrial pressure presses the two together and they fuse, leaving the fossa ovalis. A patent foramen ovale is the flap failing to fuse; an ostium secundum defect is the common atrial septal defect.
Nodes and conduction
The sinoatrial node lies in the wall of the right atrium at the upper end of the crista terminalis, where the superior vena cava enters. The atrioventricular node lies in the interatrial septum near the opening of the coronary sinus, at the apex of the triangle of Koch. The sinoatrial node fires, the impulse spreads through the atrial muscle, is delayed at the atrioventricular node so the atria finish contracting, then passes down the bundle of His through the fibrous skeleton into the septum, divides into right and left bundle branches under the endocardium, and reaches the ventricular muscle through the Purkinje fibres. The sinoatrial node is supplied by the right coronary artery in about 60% of people, the atrioventricular node in about 90%.
Chambers
The right atrium receives both venae cavae and the coronary sinus; its smooth posterior part and rough anterior part (pectinate muscles) are separated by the crista terminalis, and its appendage, the auricle, overlaps the aortic root. The right ventricle has coarse trabeculae, the moderator band carrying the right bundle branch to the anterior papillary muscle, and a smooth outflow tract, the infundibulum, below the pulmonary valve. The left atrium receives the four pulmonary veins and is mostly smooth. The left ventricle has a wall three times thicker, fine trabeculae, two papillary muscles and the aortic vestibule.
Valves
The tricuspid valve (anterior, posterior and septal cusps) and the mitral valve (anterior and posterior cusps) are held by chordae tendineae from the papillary muscles, which contract in systole to stop the cusps everting. The pulmonary and aortic valves each have three semilunar cusps that fill with blood in diastole; the coronary arteries open from the right and left aortic sinuses. The chordae and papillary muscles belong to the atrioventricular valves only.
Surface markings
The apex beat is in the left fifth intercostal space in the mid-clavicular line. The valves are heard where the blood carries their sound: aortic in the right second space, pulmonary in the left second, tricuspid at the lower left sternal edge, mitral at the apex.
Images from this station
What are you asked at the Heart 2 station?
The station runs to 14 questions over nine minutes. These are the questions as they are put to you; the model answers are in the question bank.
- Describe the embryological formation of the atrial septum
- Where are the sinoatrial and atrioventricular nodes located?
- Briefly describe how cardiac impulses are conducted
- Identify structures 1 and 2
- Identify structures 3 and 4
- Identify vessels 5-8
- Please identify the tricuspid, pulmonary and aortic valves
- Identify structures 10-13
- Identify structure 15
- What are valve are structures 17 and 18 parts of?
- What is structure 19?
- What part of the ventricles structure 20?
And 2 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 2 station ask?
It opens with "Describe the embryological formation of the atrial septum" and runs to 14 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