Everything About The Triangle of Koch (Human Cardiac Anatomy)

What Is The Triangle of Koch?

The Triangle of Koch is one of the important anatomical areas, it is located in the right atrium of the human heart, to be specific in the superficial paraseptal endocardium of the right atrium.

It is a triangle-shaped area in the right atrium of the human heart, and of the atrioventricular node, which is the beginning of the AV-bundle and it is also known as Koch triangle.

Koch’s Triangle In a Human Heart

Triangle of Koch is named after German Surgeon Walter Karl Koch,he is also a cardiologist and a pathologist. He worked as HOD at Westend hospital, Berlin and he is best known for his work on the motor centre of the human heart, and he coined the term sinus node.

Boundaries of Koch’s Triangle

  • Posteriorly, Ostium of the coronary sinus
  • Anteriorly, Septal leaflet of the tricuspid valve.
  • Antero Superiorly, Tendon of Todaro. (Tendon of Todaro is a tendinous structure connecting the valve of the inferior vena cava ostium to the central fibrous body)
Anatomical Representation of Triangle of Koch
  • Triangle of Koch ends at the site of the coronary sinus inferiorly and continuous with the eustachian tube of the human heart.
  • Membranous septum and eustachian ridge are also present near to it.
  • The Tendon of Todaro forms the hypotenuse of the triangle and the base is formed by the CSO (coronary sinus orifice) and the vestibule of the right atrium.

Contents of Koch Triangle

Koch’s triangle includes the atrioventricular node which is present at the apex of the triangle. The Triangle of Koch is also used as an anatomical landmark to locate the AV-Node.

Surgical Importance In Cardiovascular Diseases

To safely perform the radiofrequency catheter ablation within the right atrium, the triangle of Koch plays a major role by helping with the boundaries, because undesirable ablation of the AV-Node presents a risk of nodal injury and complete AV-Block.

Koch’s Triangle Dimensions

The Department of Anatomy, University of Jagiellonian Medical College, Cracow, Poland, conducted a study for the establishment of the below facts.


  1. To determine the size of Koch’s triangle.
  2. To investigate the relation between Koch’s triangle dimensions and other individual-specific and heart-specific parameters, which might be useful for clinicians.


  1. Study population
  2. Dissection and measurements 

During the study, more than 120 autopsied human hearts (randomly selected) of both sexes with a mean age of 49.317.4 years with an average measured body mass index (BMI) of 27.75.7 Kg per meter square and body surface area (BSA) 1.9 0.2 square meters were examined.

All these heart specimens were collected precisely during a routine forensic medical autopsy performed in the Department of Forensic Medicine, Jagiellonian University Medical College between July’ 2013 to October’ 2014.

The main cause of the deaths were suicide, traffic & home accidents, and murders. 

The exclusion criteria include severe macroscopic pathologies of the heart or vascular system pathologies found during the autopsy, heart trauma & macroscopic signs of cadaver decomposition.

‘None of the 120 individuals had history of any arrhythmia types.’

Dissection & Measurements

All the hearts were removed together with proximal portions of great vessels, the ascending aorta, inferior vena cava (up to 1 cm of length in each case) and all pulmonary veins.

After dissection, all the hearts were weighted and then preserved in 10% paraformaldeh

yde solution for a maximum of 2 months before the measurement time. 

All 120 heart specimens were opened in a routine way using an incision extending from the orifice of the inferior vena cava, without orifices being sectioned.

If necessary, additional cuts were made in order to present the investigated area in a better way.

Prior to measurements, all the vertices of Koch’s Triangle were marked using pins and its  edges were drawn using a permanent marker. All linear measurements were taken using a 0.03 mm YATO precision electronic calliper.

All the measurements were taken by two independent researchers in order to reduce bias.

The area of Koch’s triangle [P] was calculated using Heron’s Formula;

P =1/4(a+b+c)(-a+b+c)(a-b+c)(a+b-c)

Where a, b and c are lengths of the triangle edges. Having taken the measurements of edges and internal angles of all triangles, their correctness was tested using mathematical formulae describing a triangle and the measurements were repeated in case of deviations.

Area of Koch’s Triangle


  • KT= Koch Triangle
  • CS= Coronary Sinus 
  • IVC= Inferior Vena Cava
  • SL= Septal Leaflet of Tricuspid Valve
  • The anterior edge (a)- closed line segment bounded by the apex on the left side & the point where the basal edge touches the tricuspid annulus on the right side and tangential to the attachment line of the septal tricuspid leaflet. 
  • The basal edge (b)- closed line segment tangential to the left contour of the coronary sinus, bounded by the point where it touches the tricuspid annulus anteriorly and the eustachian ridge posteriorly.
  • The posterior ridge(c)- closed line segment bounded by the apex at the left side and by the point where the basal edge touches the eustachian ridge on the right side.


  • Koch’s triangle shows considerable individual variations in size.
  • The dimensions of the triangle are strongly independent of individual-specific and heart-specific morphometric parameters.
  • However, the maximum Koch triangle height could be determined as 22mm.
  • Anatomically significant because the AV node is located at the apex of the triangle.


Koch Triangle is the triangular area located in the right atrium with its apex as AV-Node, because of the presence of the AV-Node, proper precautions are to be taken, to prevent disturbances in the electrical activity of AV-Node and other related disorders. Heron’s formula is used to measure the area of Koch’s Triangle in the human heart.