The feasibility of left heart catheterisation and coronary angiography using small calibre 4 French catheters was assessed in a prospective register of 355 consecutive patients. The average age was 64 +/- 10 years: 21% were women. The indications were: evaluation of coronary artery disease (279 patients), control of bypass graft patency (38 patients including 34 internal mammary artery grafts), 26 valvular lesions (including 15 aortic stenoses) and 12 cardiomyopathies. In 20.5% of cases, the catheterisation was performed on an out-patient basis. The catheters used for coronary opacification were Cordis Pigtail and Amplatz; mammary, multipurpose and right Judkins were used occasionally. The operators used on average 2.14 catheters, without difficulty in 13% of cases. A larger catheter was not required in any of the cases. There were no complications. The angiograms were estimated to be of good quality in 96% of cases. With the exception of patients undergoing immediate angioplasty and 9 patients with severe hypertension or anticoagulant therapy, the patients did not require compressive dressings on the puncture site and could be mobilised early. There were no local complications at the puncture site. The results of this study suggest that 4 F catheters can be used systematically for left heart catheterisation with safety. A short period of training is required after which good quality angiograms can be obtained without technical problems. Compressive dressings are not necessary after this type of investigation.