AbstractIn 9 healthy, adult males the work intensity at pulse rate 170 (PWC170) was determined before and after i. m. injection of 0.75 mg methylscopolaminenitrate (MSN). The PWC170decreased 14 % after MSN. In 15 patients with normal circulation the effect of MSN was studied with heart catheterization at rest and during work at two progressive loads in the supine position. At rest the heart rate increased 66 %, the stroke volume decreased 34 %, and the cardiac output was unchanged. The ventricular filling pressures decreased. During work, performed after MSN, ventricular filling pressures and stroke volume increased progressively. At the highest work load the stroke volume was only 12 % lower than before MSN. Oxygen uptake, cardiac output, central blood volume and vascular resistances in the systemic and pulmonary circulations were unchanged after MSN, both at rest and during work. After MSN the heart volume, determined in the prone position, tended to decrease. The duration of the mechanical diastole, as measured from the phonocardiogram, was significantly shorter after MSN both at rest and during exercise. The investigation elucidates the relationship between the size of the stroke volume and the capacity for work at a given pulse rate and also between the size of the stroke volume and ventricular filling pressure.