Heart Shape LED Blinking
Okay. Let's go with your existing design. The NPN BJTs are rated for a maximum of about \$I_c=100mA\$ or so, so I think they should be fine. They will see a maximum load of about \$60mA\$, so within their limitations. I think those \$100\mu F\$ caps can probably manage the base currents. And also the typical \$9V\$ alkaline battery can in fact deliver \$100mA\$ if asked. So I'm going to leave everything alone except for adding in the sets of LEDs you want to insert. I'll assume that you want about \$20mA\$ in each of them. You can adjust the current limit resistors as you see fit, of course. Here's the very slightly modified schematic without the switch you added (you can work that out, I think):







simulate this circuit &ndash; Schematic created using CircuitLab

I didn't do much by way of calculation. I just figured I would use the LEDs in at most three per series chain and at least two. So this worked out to three parallel sections for each side in order to get all seven LEDs (into each side.) A very simple mental note was to divide up your \$9V\$ into 5 pieces of \$1.8V\$ each. At \$20mA\$ this works out to \$90\Omega\$ per piece. So each parallel branch has exactly five of these pieces in series. That made it very easy to work out the resistor values. If I had two LEDs in series, then I needed the resistor to account for the other three pieces (\$3\cdot 90\Omega=270\Omega\$.) If I had three LEDs in series, then I needed the resistor to account for the other two pieces (\$2\cdot 90\Omega=180\Omega\$.) That's pretty gross calculations, but it probably won't get too far from the mark. You can always just adjust from there based upon what you see.

I added a nice big cap, \$C_3\$, across your \$9V\$ battery. Try the circuit with and without it see if it makes any difference to you.

(The currents in the branches won't exactly match. So once you get it built and working, you can check to see if the LEDs are noticeably different in brightness. Hopefully not. But if so, just adjust the resistor values or insert another resistor in series to tweak them.)

That's an answer in keeping with what you wrote up, I think. I've never attempted to build this, though. And I might use a starter resistor on one side to make sure it powers up consistently. But I think it's got a shot.