In cardiovascular pharmacology, coronary artery perfusion occurs predominantly during diastole because the coronary arteries, being embedded within the myocardium, are compressed during systolic contraction. Because increased heart rate disproportionately shortens diastolic time relative to systole, tachycardia (including the compensatory tachycardia seen in heart failure) reduces total diastolic time and thus reduces coronary perfusion despite being a compensatory mechanism intended to maintain cardiac output. Beta blockers (and other heart-rate-lowering agents) improve myocardial perfusion in heart failure by reducing heart rate, thereby preserving diastolic time, illustrating a mechanism-based rationale for using negative chronotropic drugs despite their negative inotropic effects.
In cardiovascular pharmacology, coronary artery perfusion occurs predominantly during diastole because the coronary arteries, being embedded within the myocardium, are compressed during systolic cont…