This paper presents an algorithm for tracking the left ventricle in echocardiographic sequences, using multiple models. The use of multiple dynamic models is appropriate since the heart motion presents two phases (diastole and systole) with different dynamics. The main difficulty concerns the low contrast and speckle noise present in ultrasound images. To overcome this problem a robust multiple model tracker is used, based on a bank of nonlinear filters, organized in a tree structure. This algorithm determines which model is active at each instant of time and updates its state by propagating the probability distribution, using robust estimation techniques. It is shown in the paper that the proposed algorithm simultaneously copes with several dynamic models and with outliers. Furthermore the proposed algorithm provides high level information that is not available when a single model is used.