In 17 patients with coronary heart disease the influence of the beta-blocking agent 5-(3-tert-butylamino-2-hydroxy-propoxy)-3, 4-dihydro-2(1H)-quinolinone-hydrochloride) (carteolol hydrochloride, Endak, Endak mite) (0.4 mg i.v.) on heart rate, blood pressure, cardiac index, stroke volume index and pulmonary artery pressure at rest and during exercise was investigated. During exercise heart rate and cardiac index decrease significantly (p less than 0.005 and p less than 0.05, respectively). The differences in the stroke volume indices are not significant. The relationship between stroke volume index and mean pressure in the pulmonary artery shows a slight decrease after administration of carteolol at rest and a small increase of the mean pressure in the pulmonary artery during exercise. In patients with coronary heart disease left ventricular function does not change significantly at rest and during exercise after administration of carteolol.