Heart rates and systolic and diastolic blood pressures of 15 subjects were measured before, during, and after a series of four proprioceptive neuromuscular facilitation (PNF) flexibility exercises. The protocol for the study involved the use of two new machines, one designed to increase flexibility of the erector spinae, the other the hamstrings. Each machine provided constant feedback of isometric force, angular displacements, time of contraction, repetitions, and other exercise variables. Each bout of exercise involved an isometric contraction of the lengthened agonist muscle group (12 sec) followed by a concentric contraction of its antagonist in order to place the body part in a more stretched position. Hemodynamic measurements were determined at both a perceived maximal voluntary isometric contraction (MVIC) and at 50% MVIC. Significant increases in hemodynamic factors were observed when exercise measures were compared to pre- and postexercise (resting) values. Higher values, though not significantly so, were found at MVIC than at 50% MVIC on both machines. All values were well within the guidelines of the American College of Sports Medicine.