Mechanisms for improvement of cardiac performance by nifedipine in an acute mitral regurgitation in dogs.

To elucidate the mechanisms of the beneficial hemodynamic action of nifedipine in congestive heart failure, the systolic and diastolic hemodynamic parameters were evaluated for 30 min after sublingual administration of 20 mg of nifedipine in 12 dogs with acute mitral regurgitation (group 1) and in 5 dogs without mitral regurgitation (group 2, sham operation group). An additional 6 dogs with mitral regurgitation were followed for 30 min without nifedipine (group 3). Nifedipine lowered both arterial pressure and systemic vascular resistance, increased coronary blood flow and stroke volume significantly in both groups 1 and 2. The left ventricular developed tension was increased by nifedipine only in group 1, probably due to the geometric changes in the expanded left ventricle in failure, secondary to left ventricular preload and afterload reduction. Nifedipine had no effects on ventricular relaxation properties in this study. This study suggests that the mechanisms responsible for the improvement of cardiac performance induced by nifedipine in heart failure caused by an acute mitral regurgitation are essentially a reduction in left ventricular afterload and an increase in left ventricular contractility secondary to afterload reduction.