The authors made a comparative analysis of structural and functional changes of the myocardium of 21 dogs after a 30 minute limitation of the blood circulation in the circumflex branch of the left coronary artery with subsequent 30-minute reperfusion during intravenous administration of verapamil in the period and before the beginning of limitation of the coronary circulation. Verapamil produced an essential cardioprotective effect during its preventive use. The effect was less pronounced when the agent was administered after the development of ischemia.

The character of interrelationship among changes of the myocardium function, its need in blood supply and the coronary blood flow was studied in the dog isolated heart on graded increases of the left ventricle load. High perfusion pressure (PP)--13.3 kPa--made possible an adequate perfusion of the myocardium in one series of the experiments; in the second series, coronary dilatory capacity was greatly limited (PP=7.9 kPa), and in the third series coronary blood flow was significantly reduced (PP=6.0 +/- 0.25 kPa). Straight linear interrelationship only existed within the physiological range of the myocardium function and was combined with efficient left ventricle performance and adequacy of its blood supply. Overloading of the left ventricle as well as limiting of coronary dilatory capacity or coronary blood flow distorted the interrelationship, and myocardial need in blood supply greatly exceeded the actual coronary blood flow.

Coronary vascular reactivity to transitory myocardial ischemia was investigated in experiments on isolated canine heart perfused by donor blood. The investigation was performed under different cardiac functional activity regimens conditioned by a stepwise increase of volume loading. The obtained results showed that myocardial blood supply rise was accompanied by an increase in maximum reactive blood flow within the ascending arm of the ventricular function curve. On the curve plateau, a further coronary blood flow increase was combined with reduced reactive hyperemia. Left-ventricular overloading was associated with a reduction in both working hyperemia and coronary reserve. The findings demonstrate that changes in heart function are accompanied with changes in the reactivity of coronary vessels that contribute to the regulation of adequate blood supply of the heart and largely determine coronary dilative reserve and its potential realization.