Estimates of the collagen concentration in human ventricles have been made from measurements of the hydroxyproline concentration. In the normal heart the concentration of collagen was higher in the right ventricle than in the left ventricle. Age had no effect on the ventricular concentration of collagen. Hypertrophy in the absence of a valvar lesion was not associated with an increased concentration of collagen but, owing to the increased size of the ventricle, there was an increase in the estimated total mass of ventricular collagen. The concentration of collagen in the left ventricle of patients with aortic stenosis was higher than normal. Ventricular hypertrophy seems to be accompanied by an increase in the total mass of collagen whatever the cause. Whether the concentration changes or not depends on the proportion in which the mass of collagen increases relative to the mass of muscle cells.

Mitral regurgitation is a relatively common finding in coronary heart disease. In this series of 127 patients, selected with a view to coronary or left ventricular surgery on the basis of severity of symptoms, the incidence was 39 (31%). Mitral regurgitation is significantly more common in patients with a history or electrocardiographic evidence ofprevious myocardial infarction. Clinically it may present as a pan-or late systolic or even a mid-systolic, ejection type murmur at the apex or at the left sternal edge; but in 39 per cent of the patients with angiographic mitral regurgitation no murmur was present. Angiographically important mitral regurgitation (grades 2-4/4) was usually associated with a systolic murmur; this finding was independent of ejection fractions. Left ventricular enlargement clinically or radiographically is likely to accompany mitral regurgitation but left atrial enlargement (electrocardiographically or on chest x-ray) is a more reliable pointer to mitral regurgitation and pulmonary venous hypertension is even more strongly suggestive of its presence. The electrocardiographic signs of papillary muscle infarction were rare in this series (15%) and were not related to angiographic mitral regurgitation. There was no difference in the incidence of mitral regurgitation in association with anterior or inferior myocardial infarction or in distribution of coronary artery disease. There is, however, a higher incidence of mitral regurgitation in more severe coronary arterial disease (P<005).The incidence of mitral regurgitation is significantly higher with reduction in left ventricular ejection fraction (P< 0001), with rise in the left ventricular end-diastolic pressure (P<0'02), and with abnormalcontraction patterns, but the severity of mitral regurgitation is not significantly related to these findings.

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