We gave intravenous amrinone to 40 patients in heart failure, and oral amrinone to 18 patients. Acute intravenous administration caused a significant reduction in mean blood pressure and this was severe enough to require correction by plasma infusion in five patients. Oral amrinone was accompanied by thrombocytopenia in 10 patients but no complications were associated with the low platelet count. Other potentially serious adverse effects were: abdominal pain (two patients), nausea and vomiting (three patients), jaundice (one patient), myositis (one patient), pulmonary infiltrates (two patients), and polyserositis (one patient). Less serious adverse effects observed were: splenomegaly, eosinophilia, fever, headache, reduced tear secretion, dry skin, and nail discoloration. The potentially severe adverse reactions with amrinone need to be weighed carefully against its benefits in the treatment of heart failure.