Forty-six patients were randomised to receive drug (group 1) or hypnotic sedation (group 2) during percutaneous transluminal coronary angioplasty of the left anterior descending coronary artery. Intracoronary and standard electrocardiograms were continuously registered, and heart rate spectral variability was studied. Normalised units of low- and high-frequency components and the ratio of low to high frequency were measured during balloon inflations. The ST segment shifted at the first balloon inflation from 0.02 ± 0.01 to 0.09 ± 0.6 mm in group 1 and from 0.02 ± 0.08 to 0.1 ± 0.6 mm in group 2. In group 1, the low-frequency band and the ratio of low to high frequency increased significantly during the first balloon inflation (from 59 ± 10 to 75 ± 10 and from 2.4 ± 1.4 to 7.3 ± 4.7 normalised units, respectively). The increase of the ratio of low to high frequency was significantly related to ST shift (r = 0.706). In contrast, no significant variation of spectral parameters was found in group 2. The increase in cardiac sympathetic activity associated with balloon inflation and myocardial ischaemia during percutaneous transluminal coronary angioplasty of the left anterior descending coronary artery was thus eliminated by hypnosis but not by drug sedation.