Effects of cyclopiazonic acid, an inhibitor of the Ca++ ATPase of sarcoplasmic reticulum, on Ca++ transport, contraction and relaxation in cardiac muscle.

Cyclopiazonic acid is a potent inhibitor of cardiac sarcoplasmic reticulum Ca++ ATPase. It scarely affects inotropism but significantly impairs lusitropism suggesting a greater role for cardiac sarcoplasmic reticulum in the control of cardiac relaxation than in the control of cardiac contraction.