1. A phosphodiesterase inhibitor, UK 14,275 (Pfizer) was administered intravenously to six patients with suspected coronary artery disease under-going diagnostic cardiac catheterisation to assess its inotropic activity. 2. Intracardiac haemodynamic measurements included pulmonary and systemic arterial pressure. Left ventricular end diastolic pressure and left ventricular dP/dtmax were also measured, in addition to cardiac output using the indocyanine green dye technique. 3. UK 14,275 resulted in a significant increase in LV dP/dtmax and cardiac output. 4. No chronotropic action was observed using this agent. 5. This agent may have potential therapeutic value in the management of cardiovascular failure associated with low cardiac output.