It causes coronary vasodilation as well as having a positive inotropic and chronotropic effect. Diltiazem has negative inotropic, chronotropic, and dromotropic effects. Isoprenaline has positive inotropic and chronotropic effects on the heart. Contractility may be iatrogenically altered by the administration of "inotropic agents". Pharmacologic treatment with negative inotropic drugs is first-line therapy. Heptaminol is an amino alcohol which is classified as a cardiac stimulant (positive inotropic action). Negatively inotropic agents weaken the force of muscular contractions. It has a positive inotropic effect on the myocardium. Positively inotropic agents increase the strength of muscular contraction. Agents that are dromotropic are often (but not always) inotropic and chronotropic. Endothelin receptor activation mediates strong pulmonary vasoconstriction and positive inotropic effect on the heart. Hypoxia, acidosis, hyperkalemia are also negative inotropic agents. Other factors such as electrolytes may be classified as either positive or negative inotropic agents. Dihydropyridine calcium channel blockers can produce negative inotropic effects and exacerbate heart failure. Disopyramide has a negative inotropic effect on the ventricular myocardium, significantly decreasing the contractility.