In Chap. 3, the groups from Bethesda, Frankfurt, and Hamburg present data that provide considerable insights into the mechanisms of action of verapamil and other calcium antagonist drugs, as well as into the pathophysiologic mechanisms that may contribute importantly to the natural history of the disease. Thus, it is clear that verapamil diminishes the left ventricular outflow tract gradient present in those patients with the obstructive form of HCM. It does this, at least in the large majority of patients, without causing serious elevation of left ventricular filling pressures. Reduction of gradient, with resultant decrease in intraventricular pressures, undoubtedly plays a role in the beneficial therapeutic effects of this drug in patients with HCM. That this is not the only mechanism responsible for its salutary clinical effects is suggested by the fact that there is no close correlation between reduction in gradient and improvement in exercise capacity, and that patients without obstruction also improve symptomatically.