Background.To determine if weight training used during cardiac rehabilitation as soon as 4 weeks after myocardial infarction(MI) is safe, and if weight training combined with aerobic exercise improves aerobic fitness and muscle strength more than aerobic exercise alone.Methods.Twenty-three men within 6 weeks of an acute MI and without exercise-induced ischemia, complex arrhythmias, anterior Q wave MI, or ejection fraction < 40% were randomly assigned to combined weight and cycle training versus cycle training for 10 weeks. The main measures were change in maximal oxygen uptake (VO2max), muscle strength, resting left ventricular (LV) wall segment motion and early diastolic filling by resting and exercise echocardiograms, heart rate, and blood pressure responses.Results.VO2max increased 14% (P < 0.01) and cycle time increased 10% (P < 0.01) in the combined training group. The 8% increases in VO2max (P = 0.15) and cycle time (P = 0.08) in the cycling group were not significant. Arm and leg strength increased (P< 0.01) in each group. However, the change was greater for the combined training group-31% versus 16% (P < 0.03) for leg strength and 20% versus 10% (P < 0.001) for arm strength. There were no changes for either group in resting hemodynamics, body weight and composition, LV wall segment motion, LV fractional shortening, and early diastolic function, and no adverse clinical events or exercise-related complications.Conclusions.Combined training soon after MI improved aerobic and muscle fitness more than cycling alone, and was performed without complication.