Mechanical activation of the normal left ventricle (LV) is not simultaneous, however potential consequences on ejection function of the ventricle are not entirely known. We studied contraction of the LV free wall to find whether it reveals a contraction wave in axial direction during ejection. Seven guinea pig hearts in situ were studied via thoracotomy. In each heart, the ventricular and the aortic pressure were measured by two micro-tipped manometers (2-Fr, Millar). Contraction of the LV free wall was assessed with a video system (camera: Dalsa D6-0256; framegraber: EPIX PIXCI D32; acquisition rate = 500 frames/s) and epicardial markers; 15-18 markers were used for dividing the region into 20-25 triangular areas, their sizes being studied during contraction to find the position of the contraction wave. For each triangular area, two variables were determined as follows: the time (t_c) from the end of diastole until the size of the area reached 80% of maximum size reduction (normalized with duration of systole), and normalized latitude (L_ax) of the area (determined at the end diastole). A relationship between these two variables (t_c, L_ax) was determined by regression analysis. We found that the time (t_c) at which the contraction wave reached the triangular area was in positive correlation with the latitude (L_ax) of that triangular area, with a slope of 0.25±0.09 and a linear correlation coefficient 0.41±0.08. Thus, the contraction in the guinea pig's LV free wall occurs progressively from the apex to the base, with successive areas reaching 80% contraction.