The hemodynamic response and changes in myocardial contractility during leg isometric exercise with maximal exertion were studied in 30 healthy males. The exercise lasted for 6 to 8 minutes. An analysis of the results showed that the major cause of the increased arterial pressure was an increase in the stroke volume, with the systemic vascular resistance being virtually unaltered. An increased myocardial contractility was shown to be largely responsible for the elevation and the maintenance of the stroke volume at a high level. The prolongation of the sustained isometric exercise was attended by some decrease in the heart rate as compared with the first minutes and the involvement of Frank-Starling mechanism which maintains the stroke volume at the adequate level. The above isometric exercise was associated with no complications, which allows us to consider it safe for patients with heart diseases.