Hypertrophic Cardiomyopathy is an inherited condition characterized by thickening (hypertrophy) of the heart muscle. Many patients who have this condition have a reduced ability to exercise because of breatlessness, which can in some cases be severe. This appears in most cases to be due to an impairment of the filling of the heart, especially on exercise this limits the amount of blood the heart is able to pump. Several factors may contribute to this slow filling of the heart, including (1) The heart contracts and relaxes in an incoordinate way (called 'dyssynchrony') which is inefficient, and (2) The filling of the main pumping chamber (the left ventricle) may be impeded by high pressure in the other ventricle(the right ventricle)- in other words the left ventricle is 'squashed' by the right ventricle. This is known as diastolic ventricular interaction.