To determine whether a relationship exists between bronchial hyperreactivity and cardiac asthma, which is commonly observed in patients with left heart failure, a methacholine inhalation test was performed in 15 patients with stable left ventricular failure (LVF) and 10 normal subjects. The subjects were divided into 3 groups based on symptoms of nocturnal coughing and/or wheezing in acute exacerbation of LVF. Group A consisted of 8 patients with nocturnal coughing and/or wheezing, Group B consisted of 7 patients without such symptoms, and Group C consisted of the 10 age-matched normal controls. Eleven of the 15 patients with LVF showed a significant increase in respiratory resistance in the methacholine inhalation test, as opposed to none of the normal subjects. The median cumulative dose which produced a 35% decrease in respiratory conductance (PD₃₅Grs) was significantly lower in Group A than in Group B (1.45 log units and 1.90 log units, respectively, p<0 05). The results of pulmonary function tests were not significantly different between Groups A and B. The minimum cumulative dose required to initiate a decrease in respiratory conductance from the baseline, as an index of bronchial sensitivity to methacho-line, was significantly correlated with DLCO/VA (r=0.710, p<0.01). We conclude that bronchial hyperreactivity is responsible for cardiac asthma and that it might be related to pulmonary interstitial changes in stable patients with non-valvular LVF. (Jpn Circ J 1996; 60: 933 - 939)