The amplitude of the myocardial wall motion between diastole and systole was referred to as shortening (S) of the investigated region and quantified with the use of video recordings. As the ventricle was flattened, S measured at its apex represented approximately one-quarter of the variation of external perimeter during each cardiac cycle. Instantaneous contraction velocity (Cv) and relaxation velocity (Rv) were obtained from the first derivative of the shortening (dS/dt). The instantaneous heart rate (HR) was obtained from the reciprocal of the time interval between two successive systolic peaks. The velocity of the propagation of contraction (Pv) along the heart tube was derived from the delay between the mechanical events recorded at two selected levels. Precisely, Pv represented the mean velocity of propagation of the wavefront of the contraction between two selected regions, eg, atrium and ventricle.Experimental protocol: Contractions along the heart tube were recorded continuously during strictly controlled exposure of the whole heart to decreasing or increasing ramp of oxygen or to anoxia-reoxygenation transitions. Alterations of cardiac mechanical activity in response to variations of PO2 were evaluated on the basis of chrono-, dromo- and inotropic parameters. Shop online to always get proventil albuterol enjoying safe and quick shopping.