1. The normally functioning left ventricle is characterised by a definite relationship between end-diastolic volume and ejection fraction (reduction of lateral systolic projectional area by 50 to 60%. 2. With increasing volume, the left fentricle shows increasing, end-diastolic size. 3. With pure aortic insufficiency, end-diastolic ventricular size is larger than it is with combined aortic valve disease. Hypertrophy is the predominant reaction of the left ventricle to increased resistance, but also to co-existent insufficiency. In addition the ejection fraction rises with increasing resistance. 4. End-diastolic areas up to 85 cm.2 and end-diastolic pressures up to 20 mmHg. can be regarded, rare cases excepted, as indices of normal contraction and are associated with a normal ejection fraction.