heart rate during exercise while pregnant

Going on 8 weeks and I read that your heart rate shouldn't get above 140 during exercise in the first trimester. how much truth is there to this and how closely should I stick to this rule? my heart rate gets to 140 fairly quickly so I dont feel like I'm doing much 🙄 I was an avid exerciser about 5 to 6 days a week with 4 of those days being cardio but because of us focusing on TTC and I got sick I was out of the gym for about 5 to 6 weeks before finding out I was pregnant so I feel like if I go back to the gym I'll be starting over. they said you can do whatever you were doing before pregnancy but does it matter that I had taken a significant break?