Acute responses to resistance training and safety. Med. Sci. Sports Exerc., Vol. 31, No. 1, pp. 31-37, 1999. Resistance training is widely used in fitness programs for healthy individuals of all ages and has become accepted as part of the exercise rehabilitation process for patients with coronary artery disease. It is only during the past decade that the acute circulatory responses to resistance exercise have been investigated directly, using intra-arterial measurement techniques and two-dimensional echocardiography. This review examines the factors that influence the acute circulatory responses to resistance training. These include the number of repetitions, the absolute and relative load, the muscle mass engaged in the lifting, the joint angle, and the Valsalva maneuver. There is discussion of the responses in patients with coronary artery disease and the effects of resistance training on the acute responses. The review ends with a discussion of the safety of this form of exercise and concludes that it is safe and appropriate for most healthy individuals and many of those with different diseases.