FTSE 100 stocks come in all shapes and sizes. The largest are globetrotting beasts with tentacles here, there and everywhere, while some of the smallest have often just been promoted from the FTSE 250.

The thing they all have in common is an ability to make shareholders wealthier over time. Here are two established Footsie shares that I reckon are worth considering for a £20,000 ISA in April.

AstraZeneca

Let’s start with the largest of the lot, which is AstraZeneca (LSE:AZN). Currently, it has a £215bn market cap, putting it just ahead of HSBC (£206bn).

Including dividends, this world-class pharmaceuticals company has returned just over 100% in the past five years. Nice.

One thing I love about AstraZeneca is its geographic diversification. Around 40% of sales come from the US, the world’s largest healthcare market, but it also has decent exposure to China (11%) and the UK and Europe (about 15% collectively). Emerging markets revenue grew 12% last year.

Another thing to like is the reasonable valuation. Based on 2027 forecasts, the forward-looking price-to-earnings (P/E) ratio is 16.

There’s also a 1.9% yield forecast for next year. While modest, the payout is exceptionally well covered by expected earnings, suggesting the dividend should rise over time.

Then again, dividends are never set in stone. And changes in drug pricing in certain markets, as well as potential phase III trial failures, are unavoidable risks.

Stepping back, though, I’m still bullish on the stock. AstraZeneca has five multi-blockbuster cancer medicines (Tagrisso, Imfinzi, Calquence, Lynparza and Enhertu). Its oncology portfolio is growing in double digits, with Enhertu sales surging 40% last year.

We have more than 100 Phase III studies ongoing, including a substantial and growing number of trials of our transformative technologies, which have the potential to revolutionise outcomes for patients and drive our growth well beyond 2030.
AstraZeneca.

The UN predicts that the global population will reach 9.7bn by 2050, with an unprecedented ageing demographic. This is a powerful global trend for the pharmaceuticals sector.

Furthermore, AstraZeneca’s pipeline (and margins) could get a significant boost from artificial intelligence-powered drug discovery in the years ahead. I think this is currently underappreciated.

Aviva

The second blue-chip I think is worth looking at is Aviva (LSE:AV.). After its acquisition of Direct Line last year, the insurance company has over 25m customers in the UK, Ireland and Canada. More than 7m are multi-product holders.

Recently, the stock has slipped 10%, reflecting growing risks around the global economy, inflation and falling stock markets (it has a large asset management arm). However, this pullback puts the forward dividend yield at an attractive 6.8%.

Last year, group operating profit increased 25% to £2.2bn, with a target in place to achieve 11% annualised growth in operating earnings per share between 2025 and 2028. Part of this will involve repurchasing shares, starting with a £350m buyback.

Another key pillar of this growth will be more capital-light operations, particularly wealth and general insurance. Here, management says Aviva is in a “very strong position to deliver long-term growth“.

Finally, Aviva is rolling out virtual agents (agentic AI) that can handle simple claims calls from beginning to end via telephone. This tech innovation could significantly cut costs over time.

The forward P/E ratio here is just 10.5.