To investigate the correlation of haemodynamic parameters with the intensity of the gallop sound (S₃), use was made of right heart catheterization with a Swan-Ganz catheter to measure the pulmonary and right atrial pressures. The cardiac output was determined with the thermodilution method. A radiocardiogram was obtained after a bolus injection of technetium pertechnetate. The cardiopulmonary flow-index was obtained from the simultaneous recordings of the radiocardiogram and an electrocardiogram. With the haemodynamic parameters, heart sounds were recorded simultaneously and externally with a microphone. Eight Merino sheep were dosed with dried Pachystigma pygmaeum (Schltr) Robyns plant material through rumen fistulas until the clinical symptoms of heart failure such as gallop sounds, systolic murmurs and haemodynamic symptoms as well as increases in end diastolic pressure and decreases in stroke volume, appeared. After the appearance of the symptoms the sheep were treated symptomatically to delay the development of the cardiomyopathy. The changes in haemodynamic parameters before and after treatment were used and correlated with the intensity of the gallop sounds on a 6 point criterium scale. The results in brief show that, for gallop sound intensities between 0 and 6 on the criterium scale, most of the haemodynamic parameters correlate with the intensity of the gallop sounds, except the cardiac output, cardiopulmonary blood volume and the systemic and pulmonary vascular resistances. The haemodynamic parameters correlate better with the intensities of the gallop rhythm between 0 and 3. It is evident from this study that the model of heart failure in sheep is useful to study heart sounds and may also be valuable in the study of the genesis of the gallop sound.