Objective To investigate the effect of low-flow inhaling NO for short time on postoperative cardiac and pulmonary functions in infants with congenital ventricular septal defect complicated with severe pulmonary hypertension. Methods Forty-five patients with congenital ventricular septal defect complicated with severe pulmonary hypertension from May 2014 to May 2016 in our hospital were enrolled. There were 19 males and 26 females, whose age ranged from 1 to 22 months (average age: 7.2±14.4 months) and weight ranged from 2.7 to 10.5 kg (average weight: 6.8±3.6 kg). The patients were randomly divided into three groups (n=15 in each): the blank group, the prior inhalation group and the posterior inhalation group. The blank group did not inhale NO, and the prior inhalation group inhalated NO for 10 min after tracheal and intubation. After the opening of the aorta, the posterior inhalation group inhaled NO for 10 min. The concentration of NO was 20 × 10–6. The pressure ratio of pulmonary circulation/systematic circulation, heart index and oxygenation index were calculated and the troponin value of the three groups was monitored 10 min after returning to intensive care unit (ICU) and postoperatively 1 h, 3 h and 24 h. Differences among above indicators between three groups were compared. Results The troponin value of the posterior inhalation group within 3 h increased most, followed by the blank group and the prior inhalation group. Postoperatively 1 h and 3 h, the troponin value of the prior inhalation group was significantly less than that of the blank group and posterior inhalation group (P<0.01) and the value on postoperative 24 h in each group was lower than that on postoperative 3 h. The cardiac index of prior inhalation group was higher than that of the blank group and the posterior inhalation group at each time point. Postoperatively 3 h and 24 has well as 10 min after returning to ICU, the cardiac index in prior inhalation group was significantly higher than that of the posterior inhalation group (P<0.05). The pressure ratio of pulmonary circulation/systematic circulation of posterior inhalation group increased more than that of blank group; the differences in two groups were significant between postoperative 3 h and 10 min after returning to ICU (P<0.01). There was no statistical significance in the pressure ratio on postoperative 24 h and 10 min after returning to ICU (P>0.05) in three groups. The index of oxygenation of the prior inhalation group was higher than that of the blank group and the posterior inhalation group and statistically different from that of posterior inhalation group (P<0.05). Conclusion Inhaling NO 10 min preoperatively can reduce the injury to the heart and lung function effectively, but the result is the opposite when inhalating NO 10 min after aorta opening.