Universidade Federal Fluminense, Niterói e Hospital Pró-Cardíaco, Rio de Janeiro

of the cardiorespiratory effects of pyridostigmine (PYR), a reversible acetylcholinesterase inhibitor. Methods- A double-blind, randomized, cross-over, placebo-controlled comparison of hemodynamic and ven-tilation variables of 10 healthy subjects who underwent three exercise stress tests (the first for adaptation and de-termination of tolerance to exercise, the other two after ad-ministration of placebo or 45mg of PYR). Results- Heart rate at rest was: 68±3 vs 68±3bpm be-fore and after placebo, respectively (P=0.38); 70±2 vs 59±2bpm, before and after pyridostigmine, respectively (P<0.01). During exercise, relative to placebo: a signifi-cantly lower heart rate after PYR at, respectively, 20% (P=0.02), 40 % (P=0.03), 80 % (P=0.05) and 100% (P=0.02) of peak effort was observed. No significant diffe-rences were observed in arterial blood pressure, oxygen consumption at submaximal and maximal effort, exercise duration, respiratory ratio, CO2 production, ventilation threshold, minute ventilation, and oxygen pulse. Conclusion- Pyridostigmine, at a dose of 45mg, de-creases heart rate at rest and during exercise, with minimal side effects and without interfering with exercise tolerance and ventilation variables. Key words: autonomic nervous system, pyridostigmine, exercise stress testing