[The mechanics of heart diastole]

In one of the two series of experiments on dogs, the ECG, tensocardiogram of the external obliquus and circular muscles, aortic pressure and pressure in the heart left and right ventricles were recorded. In the 2nd series of 7 experiments, X-ray markers were introduced into the muscles of ventricles' walls for X-ray pictures of the heart during systole and diastole with subsequent measuring of distances between the markers. The data obtained showed contraction of the external obliquus and internal straight muscles in phases of reduced expulsion, isovolumetric reduction of the intraventricular pressure and fast filling, the contraction securing a smooth decrease in the intraventricular pressure, a change in shape of the ventricles and their sucking action. The contraction of the above muscles entails electrical phenomena during diastole recorded in the ECG as the U peak.