The sino-atrial node was observed in 23 dog hearts with serial slices. The sino-atrial node lies below auriculocaval junction, beneath the epicardium of sinus venosus by the side of the sulcus terminalis. The shape of the sino-atrial node is a long spindle with a greater upper part and a thiner lower part. Its central area is located near the junction of upper 1/3 and middle 1/3. Its size is 11.06?2.95?1.16mm, The sinoatrial node artery penetrates through the sino-atrial node only in 6 cases. In others, it may be located in sinus venosus side, the atrial side of the node or in the deep myocarium. Within the sino-atrial node there are chiefly P-cell ane T-cells. The P cell is small with greater nuclear, light colored, and formes clusters which present themselves in the centre of the sino-atrial node. The size of the T cell is between P cell and the myocardial working cell and is situated on the peripery of the sino-atrial node. In the sino-atrial node there are large numbers of collagen fibers. The nerve fiber ls appear more abundant near the lower part of the sino-atrial node.

Objective To observe the cellular morphologic features of coronary sinus orifice(CSO) and its peripheral myocardium and discuss its functional significance in radiofrequency ablation atrial reentrant arrhythmias and AVNRT. Methods A total of 7 out of 15 cases were observed by means of autopsy, and serial sections of 7 cases of adult hearts in sagittal plane were stained with HE and Mallory staining. The cellular features of different muscular fibers and their arrangement were observed under light microscope; one case was studied under electron microscope. Results CSO and the majority of coronary sinus were encompassed by atrial myocardium; CSO fibers toward posterior was connected with extension of terminal crest (CT); and supravalvular muscular ring of right atrium(RAMR) and that toward anterior was connected with AVN. P cells were seen in superior-anterior and inferior-anterior wall of CSO. A lot of T cells were discovered on the inferior wall of CSO. Purkinje cells were mainly found in the superior wall of CSO. The muscular fibers from CSO to AVN were composed of T cells and dissected into two parts: the first one was called right atrial nodular bundle and the second one posterior node extension which was identical with the ablation target of slow pathway. In addition, lots of nerve fibers were seen in myocardium of CSO adjacency particularly in the tissue of the posterior wall of CSO. Conclusion Myocardium of CSO adjacency may belong to slow pathway of DAVNP. The myocardium of CSO adjacency participates in the formation of circular pathway in atrial reentrant arrhythmias and AVNRT. It is possible that CSO is an important latent pacing maker.

The morphology and position of the AV node and AV bundle were observed in 13 human hearts with serial sections. 1.the AV node is a long sagittal flatt ened structure, its transverse section is triangular in shape with a right convex surface, sometimes the cross section is fusiform or half oval in shape. Its size is 3.5x3.3x1.1 mm in adult. In 5 cases the endocardium lying on the right surface of the AV node is elevated.2.The AV node is situated in the upper border of the atrioventricular septum (between the levels of the attachment lines of the mitral and tricuspid valves). The adult AV node is 1.8-5.8 mm anterior to the coronary sinus orifice, 0.3-0.7 mm from the endocardium of the right atrium, 3.3-7.5 mm above the upper border of the septal leaflet of the tricuspid valve. The left surface of the AV node contacts with the central fibrous body.3.The AV node can be divided in 2 parts: superficial and deep, the fibers of the super ficial part are longitudinal in sections and end in the lower border of the AV node. In one case, the deep part is subdivided in an upper part and a lower part. In the specimens in which the right atrial endocardium lying on the right surface of the AV node is elevated, the overlaying fibers end in the endocardium. At the upper border, right surface, and posterior margin of the AV node, there are atrial fibers ending to the AV node. 4. The adult AV bundle is 5.7-7.9 mm long, 1.1-1.5 mm in diameter. Its anterior part is on top of the muscular interventricular septum in 7 specimens, on its left surface in 3 specimens, and in the substance of the muscular interventricular septum in 2 specimens. In one case its course is very special, at first on the top of muscular interventricular septum, then at its left surface, finally in the substance of the right part of the muscular interventricular septum.

Using the angiography and the corrosion methods we studied the arterial distribution of the papillary muscles of the left ventricle in llo dog hearts, according to the peculiarities of vasculature, disscused the influence of obstruction of coronary artery upon the papillary muscle.The anterior and posterior papillary muscles in dog all are tethered type. The average length and width of anterior papillary muscle are 1.96 cm. and 1.10cm, respectively, while those in the posterior papillary muscle are 2.04 cm. and 1.20 cm. respectively.The origins of arterial blood supply of anterior papillary muscle may be classiffied into 4 types, type Ⅰ, in which the arterial branehes are from the anterior descending artery, is in leading position(71%); type Ⅱ, in which branches are both from the anterior descending and left circumflex arteries, is in the next place(18%). Origins of arterial branches of posterior papillary muscle are classed under 2 types: type Ⅰ, in which all arterial branches are from the left circumflex artery, is the most, 91%, among them 65% from the posterior branch of the left ventricle.The peculiarities of arterial distribution in papillary muscles are as follows: 1. All artery branch entering the papillary muscle are of Class B. 2. All are segmental distribution in papillary muscles. Each muscle recieyes 2-9 branches, mostly 5 or 6 branches. 3. Each half of one papillary muscle recieves several branches symmetrically. 4. The arrangement of hrauches may be classiffied into several types; mixed type is the most, then comes the transverse type. 5. The branches anastomose each other to form the subendocardial plexus, which is most evident in the middle and upper third of the papillary muscle.

This thesis is the study of the morphology and arterial supply of the papillary musclcs of the left ventricle of 104 human hearts. The maim me-thod used is angiography and corrosion. The commonest number of the anteri-or and posterior papillary muscles is one. In 72 hearts there are musculartrabeculae by which the papillary muscle is attached to the wall of the leftventricle. The projection of the auterior papillary muscle of the left ven-tricle on the heart surface lies most frequently on the middle third regionof a supposed "#"-form region. There are three types of attachment of thepapillary muscle: the free, the attached and the intermidiate, among whichthe largest number is the first type. The arteries supplying the anteriorpapillary muscle are the branches of the anterior descending artery, theleft circumflex artery or these two. Each of the three types amounts to30% or so; the posterior papillary muscle is mostly supplied by the leftventricular posterior branches of the right circumflex artery 9.6 % ). The blood vessels in the papillary muscle belong to class B, each of the papillarymuscles containing 1--3 major vessels measured 0. 1--1 mm in diameter.The three vascular distribution types in the papillary muscle are of axis,segment and mixtnre, and the axial type is most commonly seen of all. Thevascular distribution type j? of certain relation to the attachment type ofthe papillary muscle. The axial distribution is frequently found in the freetype of the papillary muscle. The arteries distributes on either side of thepapillary muscle.