Cypermethrin is widely used as an insecticide on animals and in agriculture, the home, and the garden. The effect of inhaled cypermethrin on the cardiac mechanics, electrophysiology, and ultrastructure in frogs was investigated in this study. Four groups received 100 muL of cypermethrin via inhalation for different exposure times, and one group was used as a control. Electrical and mechanical activities of the heart were recorded, and heart samples were examined at light and transmission electron microscopic levels for all groups. The atrial and ventricular contractile forces on the mechanogram, the amplitude of the P wave and the QRS complex on electrocardiogram, and the heart rate were significantly decreased in cypermethrin-inhalated frogs. The total duration of contraction was prolonged in the study groups. Ultrastructurally, dilatation in smooth endoplasmic reticulum cisterns, a decrease in the number of mitochondria, disorganization in the myofibrils of myocytes, and necrotic changes in endothelial cells were observed. These results suggest that cypermethrin has cardiotoxic effects that increase with exposure time. (C) 2003 Elsevier Science (USA). All rights reserved.