Highland mountain hiking and coronary artery disease: exercise tolerance and effects on left ventricular function. Med. Sci. Sports Exerc., Vol. 29, No. 12, pp. 1554-1560, 1997. Physical exercise has become a well-established concept in the secondary prevention of coronary artery disease. We investigated the exercise requirements of extensive highland mountain hiking (8.7 km, 470 m to 1220 m over sea level, average incline 8.5%, mean walking velocity < 3 km·h-1) in 11 regularly exercising male patients with history of MI and stable coronary artery disease (CAD; mean age ± SD:61.0 ± 3.9 yr) and 9 age-matched male healthy controls(CO; mean age ± SD:61.2 ± 5.0 yr). All subjects underwent continuous ECG monitoring; arterial blood pressure and blood lactate concentrations were measured several times during mountain hiking. Before and after exercise, cardiac dimensions and functions were assessed by two-dimensional echocardiography and Doppler echocardiography. The mean exercise levels for heart rate and blood lactate were compared with the corresponding data of a multistage upright cycle ergometry. Clinical manifestations of coronary insufficiency, left ventricular myocardial dysfunction, or cardiac arrhythmias > Lown IIIb were not observed in any case. No significant differences in left atrial and left ventricular dimensions and no changes in systolic left ventricular function compared with the preexercise values were found after the mountain hike tour. Doppler echocardiography demonstrated significant changes in diastolic left ventricular function in CAD, but not in CO. The peak exercise intensity during mountain hiking was equivalent to a workload of 100-125 W (1.25-1.5 W × kg-1 body weight) in a multistage upright cycle ergometry. Extensive highland mountain hiking may be a low risk alternative within the outpatient rehabilitation program for secondary prevention of CAD for MI patients with a cycle ergometric exercise tolerance > 1.5 W × kg-1 body weight.