I. Mechanism of Action
II. Available Calcium Antagonists
III. Therapeutic Benefits
IV. Next Generation Agents
GLOSSARY
angina pectoris short duration, recurrent chest pain or pressure often accompanied by feelings of suffocation and impending doom; most frequently associated with lack of blood and oxygen to the heart muscle.
arrhythmia general term for an irregularity or rapidity of the heartbeat, an abnormal heart rhythm.
ejection fraction the fraction of blood ejected from the heart into the arteries, normally this ranges from 60 to 75%; a low ejection fraction is less than 40%; often used as a marker of left ventricular contractility.
heart failure failure of the heart to pump sufficient blood from the chambers into the aorta; an inadequate supply of blood reaches organs and tissues.
inotropic an effect that affects the force of muscular contrac¬tions; negative inotropic refers to decreased myocardial con¬tractility that may lead to poor pumping of blood, reduced ejection fraction, and heart failure.
myocardial infarction death of an area of heart muscle due to blockage of a coronary artery by blood clot and atheroma; medical term for heart attack or coronary thrombosis.
myocytes single muscle cells.

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• I. MECHANISM OF ACTION
  Calcium movement into cells is mediated by several mechanisms. Albrecht Fleckenstein showed that the calcium channels can be selectively blocked by a class of agents. He called these agents calcium antagonists. Calcium movement into the cells is mediated by several mechanisms. Calcium antagonists act at the plasma membrane to inhibit calcium entry into cells by blocking voltage-dependent calcium channels.
• II. AVAILABLE CALCIUM ANTAGONISTS A. Dihydropyridines
  These agents cause dilation of arteries throughout the body including mild dilatation of coronary arteries. They also cause a variable decrease in myocardial contractility that may lead to heart failure in susceptible individuals.
• IV. NEXT GENERATION AGENTS
  Several dihydropyridine calcium antagonists have been introduced during the past 25 years. First degeneration dihydropyridines are the naturally short-acting agents that include felodipine, isradipine, nifedipine, and nitrendip-ine. These rapid-acting vasodilators are powerful anti-hypertensive agents, but their fast onset of action results in marked vasodilation that causes reflex stimulation of the sympathetic nervous system and hemodynamic adverse effects that include increased heart rate, increased cardiac workload, and an increased incidence of heart failure in patients with left ventricular dysfunction. These adverse effects have become controversial and the short-acting formulations of dihydropyridines such as verapamil and diltiazem are no longer recommended. They have largely been removed from the marketplace.
• BIBLIOGRAPHY
  Khan, M. Gabriel. In Cardiac Drug Therapy, sixth edition, W. B.