Two days rest a week if you're working out hard, your body needs the time to repair. Muscles (including the heart), get bigger/stronger through the process of getting tiny little tears in them when you work them and then rebuilding those tears bigger/stronger than they were before. If you don't give yourself the rest time you're not giving your body the opportunity to repair itself and rebuild stronger.
That soreness is a sign that your body needs the time to rebuild, so you did the right thing by laying off the weights. If you try and push yourself too hard everyday then your body won't be able to rebuild and you won't be able to train as hard meaning you're slogging away in the gym everyday feeling like you're ttraining really hard but actually getting nowhere.
Try and get 50g of protein down you as soon as you finish training too, within 30 minutes if you can but within the hour if not.