Palpitations high heart rate. Also.

Hello anyone please clear my doubt, while walking just few seconds my heart rate goes to 120-140 .every evening I do walking for 3 kms in that my heart rate went to 170 max . I have done 2d echo lot of ecgs and Holter also . While resting it will between 70-90 . And very high heart palpitations while sleeping , please I'm trying for loosing weight ,I'm afraid about high heart rate for that im stopping doing exercise , is it okay that going 170 while doing brisk walk for 30 mintues , is it okay to stay in 160 BPM for 30 mins, and after stopping exercise my heart rate comes to 100-105 with in 3 minute' . Please help me that is it normal variation or should I concern for anything ,I have attached Holter report also .