The effects of intracoronary administration of ionic and nonionic contrast materials on (LV)left ventricular contractile state, relaxation rate (peak -dp/dt and [-dp/dt]50), and dimensions were determined in eight morphine-chloralose anesthetized dogs. Meglumine sodium diatrizoate caused decreases in peak dp/dt and -dp/dt and increases in left ventricular end systolic dimension (LVESD'), end diastolic dimension (LVEDD'), and end diastolic pressure(LVEDP). The decreases in peak -dp/dt and(-dp/dt)50 persisted after peak dp/dt returned to and exceeded control levels. Calcium meglumine sodium metrizoate caused increases in peak dp/dt but decreases in peak -dp/dt and(-dp/dt)50 and no significant changes in LVEDP, LVESD', or LVED'D. Metrizamide caused no significant changes. Ionic contrast materials induce important changes in LV dimensions and rate of relaxation in addition to producing a depression in contractile state. The decreases in relaxation rate are not reversed by addition of calcium ions.