The sino-atrial node is situated at the junction between the atrium proper and the sinus venarum of the fight atrium, inclined to the wall of the sinus venarum and covered only with the epicardium.

No A-V anastomosis could be seen, yet thebesian vessels and myocardial sinusoids directly opened into ventrical chamber could be found.

All of them received three chamber biventricular pacing and the left ventricular pacing lead was inserted into a cardiac vein through coronary sinus.