Welcome to HCM ,
while passing motion if you strain it will cause extra burden on heart and it will cause raise in BP and tachycardia
i would like to suggest never ever strain while passing motion / during toilet ,
make sure that you should not have constipation
any time ,
to prevent constipation take more green leafy vegetables , high fiber diet , fresh fruits , adequate water,
be in regular follow up with your cardiologist and adjust medicine as per his advice .