To increase muscle mass and strength in patients with chronic congestive heart failure (CHF), there is a need for implementing resistance exercises in exercise training programs. This study sought to assess the safety of rhythmic strength exercise with respect to left ventricular function in 9 patients with stable CHF, compared with 6 stable coronary patients with mild left ventricular dysfunction (control group). With use of right-sided catheterization, changes in left ventricular function were assessed during double leg press exercise at loads of 60% and 80% of maximum voluntary contraction. The exercise sessions lasted 14 minutes each, divided into work and recovery phases of 60/120 seconds. In CHF, during exercise at a 60% load, there was a significant increase in heart rate (mean ± SEM 90 ± 4 beats/min; p <0.05), mean arterial blood pressure (95 ± 3 mm Hg; p <0.01), diastolic pulmonary artery pressure (20.2 ± 2.7 mm Hg; p <0.01), and cardiac index (3 ± 0.3 L/m²/min; p <0.05). Additionally, during leg press exercise at an 80% load, there was a significant decrease in systemic vascular resistance (1,086 ± 80 dynes · s · cm⁻⁵; p <0.001), an increased cardiac index (3.4 ± 0.1; p <0.001), and left ventricular stroke work index (75 ± 5 g · m/m²; p <0.01), suggesting enhanced left ventricular function. Compared with controls, in CHF the magnitude of changes in hemodynamic parameters during exercise, demonstrated at a 60% load, was significantly smaller (systemic vascular resistance: [mean] 1,613 → 1000 vs 1472 → 1,247 dynes · s · cm⁻⁵; cardiac index: 2.4 → 3 vs 2.8 → 4.4 L/m²/min, and stroke work index: 60 → 69 vs 114 → 155 g · m/m²; p <0.05 each). Nevertheless, changes indicated an enhanced contractile function of the left ventricle in CHF. This study demonstrates stability of left ventricular function during resistance exercise in well-compensated CHF patients with optimal drug therapy, as well as the appropriateness of the chosen mode and intensity applied as these factors relate to cardiovascular stress. This conclusion cannot be extrapolated to patients with less well-compensated heart failure, or to more protracted resistance training.