The effects of 12 weeks of low intensity physical conditioning on serum lipid levels, body composition, and cardiorespiratory function were studied among patients with coronary heart disease. Twenty-three men, 45 to 59 years old, volunteered to participate. Three were excluded for medical reasons, and one voluntarily discontinued exercise. The conditioning program included a 10-minute warmup, 15 to 30 minutes of walking-jogging at an individually prescribed intensity corresponding to 70% to 75% of maximum heart rate (HRmax), and a 5-minute recovery period. The conditioning resulted in a decrease (p less than 0.05) in heart rate and blood pressure during standard submaximal work (200 kg/m/min). Maximal heart rate increased (p less than 0.05) by five beats per minute. Symptom-limited maximal oxygen uptake increased 12.8% (p less than 0.001) when expressed per unit body weight. Body weight remained essentially unchanged (-0.34 kg), while fat-free weight and fat weight increased (+0.68 kg, p less than 0.05) and decreased (-1.02 kg, p less than 0.05), respectively. Serum lipid levels remained unaffected by the conditioning regimen. Low intensity exercise is effective in cardiac reconditioning and should be favored at least during the initial stages of a training regimen in view of the decreased orthopedic problems, added safety, high adherence level and tolerable working rate.