We examined the effects of four kinds of intravascular contrast agents (amidtrizoic acid, iohexol, iopamidol, and ioxaglic acid) on [Ca2+]i transients (indo-1 fluorescence) and cell contraction (video motion analyzer), using cultured chick embryo ventricular myocytes. Exposure of ventricular myocytes to amidtrizoic acid (a conventional contrast agent) reduced the [Ca2+]i transients and the sensitivity of the contractile elements to [Ca2+]i. Ioxaglic acid (a low osmotic contrast agent) also reduced the [Ca2+]i transients, but did not significantly change the sensitivity of the contractile elements to [Ca2+]i. Neither iohexol nor iopamidol (nonionic contrast agents) reduced the [Ca2+]i transients, but both significantly decreased the sensitivity of the contractile elements to [Ca2+]i. A marked negative inotropic effect of amidtrizoic acid was caused by both calcium binding and hypertonicity. The less marked depression of contractility produced by ioxaglic acid is possibly the result of calcium binding, but is not caused by hypertonicity. The negative inotropism produced by nonionic contrast agents (iohexol and iopamidol) was due to hypertonicity, but not due to alterations in the [Ca2+]i transients. Exposure of ventricular myocytes to nonionic contrast agents (iohexol and iopamidol) slowed decay in the [Ca2+]i transients with increased end-diastolic [Ca2+]i. After washing out the nonionic contrast agents, these parameters returned to control levels. On the other hand, exposure to amidtrizoic acid decreased end-diastolic [Ca2+]i without changing decay time in the [Ca2+]i transients. After washing out amidtrizoic acid, there was a prolongation of half decay time in [Ca2+]i transients with a significant increase in end-diastolic [Ca2+]i and cell position. Diastolic dysfunction just after washout of amidtrizoic acid was possibly caused by an increase in [Na+]i due to sodium influx during exposure to the contrast agent.