Left ventricular dimensions and function were estimated in 11 healthy volunteers by means of echocardiography during isometric exercise and the Valsalva manoeuvre. Isometric exercise induces a rise of heart rate and Vcf by 14% and of cardiac output as well as of the cardiac index by 12%. Stroke volume remains unchanged. During Valsalva's manoeuvre a marked decrease in left ventricular dimensions is observed. A reduction of the stroke volume by 29% was not compensated by increasing heart rate. However, cardiac output and cardiac index is found 10% below control values.