Effect of timolol on blood flow distribution in the myocardium during acute regional ischaemia in cats.

The beta-adrenergic blocking agent timolol was given to cats with acute coronary artery ligation. Regional myocardial tissue flow was measured by the distribution of 15 micrometers labelled microspheres. Timolol reduced heart rate, cardiac contractility and left ventricular systolic pressure, but end-diastolic pressure rose. Ischaemic tissue blood flow remained unchanged following timolol, thus improving the marked imbalance between oxygen demands and delivery. In normal areas of the myocardial tissue flow was reduced, indicating the beta 2-adrenergic blocking effect of timolol. This was also the case for the border area between ischaemic and non-ischaemic tissue, but significantly less flow reduction was found on the endocardial side than on the epicardial side in the border area. Except for this latter observation, timolol does not appear to improve coronary perfusion. The present study, therefore, indicates that beneficial effects of timolol on ischaemic myocardium are mainly related to a reduction of myocardial oxygen demand.