In order to analyse the response of the right ventricule (RV) to transient myocardial ischaemia, the RV ejection fraction was measured using a new rapid response thermodilution catheter in 15 patients (14 men and 1 woman: average age 58 +/- 7 years) referred for percutaneous transluminal coronary angioplasty of a dominant right coronary artery. Only patients with single vessel disease with a proximal stenosis of the right coronary without a visible collateral circulation who had no previous history of myocardial infarction were included. Right heart catheterisation was performed with a rapid-response thermodilution catheter which enabled measurement of heart rate, cardiac index, RV end-diastolic and end-systolic volumes and RV ejection fraction. Angioplasty was carried out with the usual steerable balloon catheters. During balloon inflation, there was a slight increase in RV end-diastolic volume (from 78 +/- 11 ml/m2 to 85 +/- 13 ml/m2 at 60 seconds; p less than 0.01) and a large increase in RV end-systolic volume (from 29 +/- 8 ml/m2 to 35 +/- 8 ml/m2 at 30 seconds and 43 +/- 11 ml/m2 at 60 seconds, p less than 0.001) leading to a significant decrease in RV ejection fraction (from 62 +/- 8% to 56 +/- 6% at 30 seconds and 51 +/- 7% at 60 seconds; p less than 0.001). All parameters returned to basal values two minutes after the dilatation. Acute occlusion of the proximal segment of the right coronary artery is therefore associated with a marked change in right ventricular function which rapidly returns to normal after the coronary circulation is restored.