The invention relates to pimobendan for use in a method of reducing the heart size and/or delaying the onset of clinical symptoms in a patient suffering from asymptomatic (occult, preclinical) heart failure, preferably congestive heart failure, due to mitral valve disease (MVD), and/or delaying the onset of heart failure, preferably congestive heart failure, in a patient suffering from asymptomatic (occult, preclinical) heart failure, preferably congestive heart failure, due to mitral valve disease (MVD), wherein the patient is preferably a mammal, more preferably a human, a dog, a cat or a horse, and most preferably a dog.