A 45-year-old male with palpitations and a heart murmur was investigated. Echocardiography and haemodynamic study revealed the presence of a ostium primum type interatrial communication with left-right shunting and asymmetric hypertrophic heart disease. There was no subaortic obstruction, but anterior systolic movement of the mitral valve was detected that did not contact with the interventricular septum--in part due to the paradoxical motion of the latter. The possible benefit of surgery in this infrequent association is discussed, and a review is made of the literature.