This climb follows the Castle Lake Trail east of the lake until you split off to traverse west when you come to the depression/mini valley that Heart Lake sits in.
The north facing slope that forms the south side of the Heart Lake "valley" can get some gnarly looking cornices that do drop, and it's easy to see plenty of slide debris/ paths. So I try to stay on the west to east running ridge on the north side of the "valley" to minimize the risk.
That puts you onto a S-W running ridge that will take you to the summit. The last little bit of the ridge kicks up in angle that isn't reflected on the digital elevation profile (when I did it in the spring, I started to wish that I had some pointy bits). It was enough to have to kick out step as to not slide down the slope. There is a nice flat area on top to transition and head down your preferred route.
Most people head down the face/bowl that comes into the SW corner of the lake.
You'll enjoy fantastic views of Shasta if it's clear. Also, you get to look down into Castle Crags and over to Mt. Eddy.