The incidence of coronary heart disease (CHD) rises annually [1] According to global health assessments, CHD is responsible for 16.6% of all mortality globally [2]. It is assessed that 11.06 million individuals currently are living with CHD [3]. Three principal manifestations of psychological distress are depression, anxiety and perceived stress, which have a causal relationship with CHD and its adverse effects [4-6]. Psychological distress is prevalent among CHD patients; to illustrate, depressive symptoms are concomitant conditions among 40% of CHD patients [7]. In a systematic review, the rate of co-occurring anxiety disorders with CHD on average was as high as 16% [7], and stress perceiving was as high as 50% [8]. Anxiety, depression, and stress can induce abnormal coronary contractions [9]. Also, acute and chronic psychological distress can cause the development of multiple coronary issues [10] and elevate the rate of re admission to the hospital even after the healing time, morbidity, and mortality among CHD patients [11]. There is mounting evidence indicating that psychological distress, exclusively depression, has been acknowledged as a recognised risk factor for its deleterious and prevalence influence on CHD patients [11]. It is also known for its correlation with poor prognosis of CHD patients [12]. A study conducted by Bijing and his colleagues indicated that each psychological distress variable(depression, anxiety, and stress) separately and considerably predicted deterioration in physical functioning, with its impact being consistent at six and twelve months [13]. For instance, perceived stress inversely correlated with physical functioning in coronary heart patients as well. There is emerging evidence indicating that targeting psychological distress is a robust predictor of changes in clinical outcomes. For specific, targeting stress and anxiety through a stress management program [14] or complementary interventions [15, 16] can diminish cardiac risk and enhance well-being. Several studies conducted to determine the impact of changes in psychological distress on CHD patients, exclusively investigating on depression [17-19], leaves other common variables such as stress and anxiety under investigation.

Humour and laugh therapy, as a complementary therapy in the cares, via boosting the immune system, diminish tension, and increase the quality of life [20] and lessen depression [21]. A study has shown that the effectiveness of laugh-yoga in the healthy elderly population and its notable effect on the quality of life (QoL) [22]. Several compelling studies are investigating the efficiency of laugh-yoga therapy on other medical populations but CHD patients. To illustrate, on vascular function [23, 24], oncology [25], cardiology [26], rehabilitation [27, 28], cardiovascular [29] populations. In one recent study investigated the impact of implementing laughter yoga on CHD patients to determine the effect of laughter therapy on the blood glucose level, cholesterol and lipid profile levels. Which indicated respiratory laughing and relaxation work out can normalise cholesterol and lipid profile levels; therefore, should be set in the form of regular exercise besides CHD pharmacological intervention. However, this study was investigating physical variables rather than psychological distress and QoL [30].

There are several existing gaps this study wants to address on. First, most of the studies exploring the effectiveness of laugh-yoga investigated on one or two psychological distress, specifically most of them considering depression [17-19] exclusively and leaves other common manifestations such as anxiety and stress under investigation. Second, although mounting evidence implemented laugh-yoga on other medical populations [20, 22, 23], on CHD patients, the examination is scant [31]. Psychological interventions mostly employed on the modest sample, whereas this study applied the laugh-yoga on a large population-based to be reliable and facilitate the generalizability of the results to a general population.

To our knowledge, no study has investigated to determine any psychological distress changes such as stress, anxiety, and depression after employing laugh-yoga. We addressed three primary psychological distress manifestations before and after applying respiratory laughing and relaxation activities to pinpoint any changes. Simultaneously by administrating QoL questionnaire, we determined any changes, specifically in eight subscales including physical function, physical role, physical pain, general health, vitality, emotional response, mental health, social activity, and quality of life, and generally in physical function and physical role on CHD patients.

This study aimed to measure any psychological distress changes (anxiety, depression, and stress) and simultaneously determine any alterations in the quality of life after intervening laughter-yoga therapy in CHD patients.

Participants with CHD disease (N=150) was in the range from 43 to 76 years, In the control group, there were 97 women and 53 men, while in the experiment group there were 65 men and 85 women, with the total number of participants in the control group was 150, and experiment group was 150. Table 1 lists the percentage of demographic variables (sex, education, and age). The findings show that the rate of men in the control group is 35% and in the experimental group is 43%, which shows the homogeneity of both groups. Regarding the level of education in the control group, the highest rate (56% and in the control group 39%) refers to patients with high school degrees and the lowest incidence (8% in the experiment and in waiting list 6%) relates to the diploma. In terms of age, the control and experimental group were homogeneous.

Table 2 indicated The approval of the assumption of the normal distribution of variables in the test of ANCOVA. The comparison between the pretest group and all eight subscales of QoL.

Table 3 the results of the MANCOVA test consequently. In Table 3, statistical details are provided for all eight components.

The assumption of the normal distribution is confirmed (elongation values for most variables are in the range 1+ to 1- Or close to this value). We can conclude that all variables and components have a standard or near-normal distribution, and all variables can be considered normal.

The results of the study of the effect of the Wilks's lambda distribution (Multivariate Impact) showed that the value of F is 1112.56, which is significant at 99% confidence level (P<0.01), which indicates that the effect of the intervention in at least one of the dependent variables is substantial.

The intervention had significant effects on all eight components of quality of life P < 0.01. The impact of laugh-yoga on physical function, physical role, physical pain, general health, vitality, emotional role, mental health, social performance is supported by statistical significance (P < 0.01).

Table 4 indicated The Mean and Standard deviation of the quality of life subscales.

Particularly, LY has had the most significant influence on improving the subscales of physical function and mental health. The mean of QoL in the experimental group was 227.2 in the pretest; after the intervention, the variable has risen to 605.33 in the posttest significantly improved. Still, in the control group, the variable remained approximately unchanged (220.09 to 227.84).

Table 5 describes the mean and standard deviation(SD) of DASS (depression, anxiety, and stress). With a confidence level of 99% (P <0.01), we can ascertain that laugh-yoga therapy can reduce anxiety level notably. The value of T is 84.02. The mean anxiety in the pretest is 17.44, which lowered remarkably in the posttest and reached 4.20, but in the control group, the rate remained intact (16.87 to 17.80 in posttest).

The mean of stress in the pretest is 16.09, in posttest is 3.89, which degraded 13.24 after the intervention. The value of T is 75.60 and P-value less than 0.05, which was meaningful. There is a no table difference between the mean scores of cooperators in the pre and posttest. However, in the control group, no noticeable alterations occurred from 17.94 to 16.22.

Furthermore, the mean of depression in the pretest stage is 17.49 and in posttest is 4.02, which indicated a drop of 13.70. The value of T (122.90) and the P-value is <.05., but in the control group, no significant change was observed (16.70 to 18.14 in posttest).

Table 6 revealed the statistical comparisons between treatment groups of DASS (Depression, Anxiety, and Stress)

In the current investigation on CHD patients, patients in the pretest suffered from moderate depression (17.49), after undergoing the laugh-yoga therapy, their depression score comes to the normal range on average. From the clinical standpoint, several depressive manifestations improved mostly such as pessimistic viewpoint about life or enjoying or satisfying from life after participating in stimulating laughing exercises. On average participants showed severe anxiety (17.44), they had difficulty with breathing and pounding of the heart. The laugh-yoga which comprises several meditation workouts such as diaphragmatic breathing can ameliorate anxious symptoms, and participant's anxiety has upgraded to the normal state.

Furthermore, according to the stress subscale scores participants has mild stress (16.09) patients were unable to relax, irritated, and nervous, which laugh-yoga helped the stressed individuals to manage their stress notably. The results of the current study are congruent with the previous research carried out by Dr Lee Berk, whose investigation determined that laughing can reduce stress by managing secreting stress hormones [38].

The results of the current study align with the previous finding, in depression and anxiety, for specific in a study conducted by Kim in mothers [39] revealed that group laughter therapy could degrade the level of anxiety and depression in comparison to the control group. According to Chang research, the effect of LY on military stress has been shown in military patients. After three sessions of laughter, scores of anxiety, depression, and pressure diastolic blood levels in the experimental group degraded significantly in comparison with the control group [40]. On middle-aged women, laughing had a significant impact on serotonin levels and lessened the severity of depression [41].

Besides significant improved in emotional distress, the result of the current study revealed the efficiency of laughter-yoga on QoL, which is congruent with previous studies. Participants had a lower level of QoL in comparison with the general population, likewise patients with heart failure (HF), obstructive pulmonary disease [28, 42], arthritis, and other patients with a history of diabetic cardiovascular complications [41]. Also, the other corresponding previous research confirmed that a rise in the quality of life of the experimental group after intervening in the LY therapy, however the primary difference with the current research is that in that study the target population was healthy people [22]. The outcomes of the current research build upon the previous findings, confirm that LY promotes physical and psychological health-related issues among the medical population. Therefore, the result of the present study is a step forward in substantiating that simulated laughter leads to enhance the quality of life (specifical variations in the physical role) and reduce depression, stress and anxiety.

Limitation of the current research: Although the present study has a large based-population with a control group, it has not any follow-up to determine the efficiency of LY therapy over time. Additionally, most of the participants have diploma or lower than diploma education, which may affect the comprehension of the therapeutic concepts. A more educated population may get better results from duplicating this study.

According to the prevalence of the CHD in people even in advanced countries, addressing the psychological issues parallel with coronary disease, is crucial, LY therapy stimulates of doing exercise, which has a healing role not only physically but psychologically. Integrating laughter with Yoga training in the postoperative and even preoperative of CABG surgery may unload patients from emotional distress and ultimately increased the QoL, which is a primary factor in well-being. For future researches, we suggest that to intervene the LY therapy during the preoperative of CABG and other surgery, it may decrease stress-related issues and help patients to have reduced healing time after the surgery. Investigating the effect of LY on healing time, stress-related problems, and coping strategies provides further knowledge in medical populations.