Acute thrombotic obstruction of disc valve prosthesis is a rare but catastrophic event without an immediate correct diagnosis and precocious treatment (Amman et al., 1984; Assanelli et al., 1986; Copans et al., 1980; Mann et al., 1986; Gibson et al., 1974; Johnson et al., 1973; Ledain et al., 1986). That is the main reason it is important to consider each helpful sign in order to recognize such a situation. We detected an important dilatation of the right ventricle in two patients with different stages of thrombosis of mitral Björk, the first one had also a chronic dilatation of the right ventricle due to tricuspid regurgitation. The clinical and pathophysiological aspects of these unusual situations are described in this article.