Weight loss after heart attack. Guide!

I had heart attack in September and after that I have made number of changes in my lifestyle.This has resulted in weight loss of around 7- 8 Kg in last seven months.Earlier my weight was 78 kg and now it is around 71.5 kg.I regularly go to gym and do treadmill for 40 min and cyling for 20 min.This i am doing everyday. I have lost lot of belly fat also.My EF is 50-57% as measured during stress test in January. My question is whether lossing this much weight is harmful as visibly i have started looking weak.Reduction of weight has also made all my clothes look very loose.Although physically i feel fitter than before. but visually i look weaker. Should i stop doing excessive exercise and start eating more so as to gain some weight.Kindly guide